Scalable and modular automated fiber optic cross-connect systems

ABSTRACT

This invention discloses patch-panel systems for organized configuration management of large numbers of fiber optic interconnection strands, wherein each strand transmits high bandwidth signals between devices. In particular, a system for the programmable interconnection of large numbers of optical fiber strands is provided, whereby strands connecting a two-dimensional array of connectors are mapped in an ordered and rule based fashion into a one-dimensional array with substantially straight lines strands there between. The braid of fiber optic strands is partitioned into multiple independent, non-interfering zones or subbraids. The separation into subbraids provides spatial clearance for one or more robotic grippers to enter the free volume substantially adjacent to the two-dimensional array of connectors and to mechanically reconfigure one or more optical fiber strands without interrupting or entangling other fiber optic strands.

FIELD OF THE INVENTION

This invention relates to optical systems using fiber optic cables totransmit illumination and/or signals, and more particularly, to highport count, scalable, modular and automated optical cross-connectdevices enabling reconfigurable and programmable connections betweenfiber optic cables.

BACKGROUND OF THE INVENTION

Fiber optic patch-panels are used to terminate large numbers of opticalfibers in an array of connectors mounted on modular plates, therebyproviding a location to manually interconnect patch cords for theirrouting to adjacent circuits. Splice trays within the panel retain slackfiber and the splices joining connector pigtails to the individual fiberelements originating from one or more cables. Typical patch-panelsystems interconnect 100 to 10,000 fibers. Connection to various typesof transmission equipment, such as transceivers, amplifiers, switchesand to outside plant cables destined for other exchanges, local offices,central offices, optical line terminations and points-of-presence areconfigured manually at the patch-panel.

As the reach of fiber optic systems extends to FTTH (Fiber-to-the-Home),access and enterprise networks, the locations of patch-panels arebecoming geographically more dispersed and the sheer numbers of portsare increasing dramatically. Consequently, the tasks of allocating,reconfiguring and testing a fiber circuit within the network becomesincreasingly challenging because of the potential for errors or damageresulting from manual intervention. Remotely reconfigurable patch-panelsreduce the operational and maintenance costs of the network, improve thedelivery of new services to customers and leverage costly test anddiagnostic equipment by switching or sharing it across the entirenetwork. Therefore, it is appealing from a cost, accuracy andresponse-time perspective to configure the patch-panel automaticallyfrom a remote network management center. The key building block of anautomated patch-panel system is a scalable, high port count, all-opticalcross-connect switch.

A wide range of technologies has been developed to provide opticalcross-connect functionality with several hundred ports. These includearrays of steerable micro-electromechanical (MEMS) mirrors to deflectbeams, piezoelectric steerable collimators that direct free space beamsbetween any pair of fibers, and complex robotic cross-connects utilizingactuators that reconfigure fiber optic connections. For the purpose ofcomparison the first two approaches as categorized as “non-robotic” andthe latter approach as “robotic”.

Non-robotic cross-connect switches, while offering the potential forrelatively high speed (10 ms), do so at the expense of limited opticalperformance and scalability. The coupling of light into and out-of fiberand free-space introduces substantial alignment complexity andsignificantly increases insertion loss, back reflection and crosstalk.These approaches also require power to maintain active alignment andintroduce micro-modulation of the transmitted signal as a result of theneed to actively maintain mirror alignment. As a consequence, MEMSswitches do not provide an optically transparent, plug-and-playreplacement for manual fiber optic patch-panels.

Robotic cross-connect approaches perform substantially better from thestandpoint of optical performance and their ability to maintain signaltransmission even in the absence of power. However, the scalability ofsuch approaches has been limited. The footprint of prior art roboticswitch designs scales as N², where N is the number of circuits. The sizeof the switch matrix is typically N columns by N rows wide with N²possible interconnection points. Considering that the central offices oftoday's telecommunications service providers already utilize 1000 to10,000 port patch panels, scalability is of prime importance. Therefore,an approach scaling linearly in N would enable the cross-connect toachieve a substantially higher port density commensurate with manualpatch-panels.

Moreover, typical network installations are performed in an incrementalfashion, whereby fiber circuits are added to the system as needed.Robotic and non-robotic approaches have not been modular and as such,they do not offer an upgrade path from 200 ports to 1000 ports, forexample. To achieve port counts above several hundred, a three-stageClos network interconnection scheme must be implemented [C. Clos, “Astudy of non-blocking switching networks” Bell System Technical Journal32 (5) pp. 406-424 (1953)], leading to a substantial increase in cost,complexity and a reduction in optical performance by virtue of the needto transmit through a series of three rather than one switch element.

In addition, the optical performance of robotic cross-connects, whileimproving on non-robotic approaches, is still inferior to manualpatch-panels because they introduce an additional reconfigurable fiberoptic connection in series with each fiber circuit. A manual patch-panelrequires only one connector per circuit and offers a typical loss of<0.25 dB, while the equivalent robotic patch-panel incorporates at leasttwo connectors per circuit. This increases the loss by a factor of 2.

Furthermore, robotic approaches have required significant numbers ofprecision, miniature translation stages (2N) and at least 4 precisionrobotic actuators to align large numbers of input and output fiber endfaces to one another. These fiber end-faces physically contact oneanother and can exhibit wear-out for switch cycles in excess of 1000, orcan become damaged at the high optical power levels transmitted throughfiber in Raman amplified systems. The performance of frequentlyreconfigured test ports is therefore susceptible to degradation.

The prior art describes various mechanized approaches to interconnectinga number of fibers. U.S. Pat. No. 5,699,463 by Yang et al. discloses amechanical optical switch for coupling 1 input into N outputs bytranslating an input fiber and lens to align to a particular outputfiber. For patch-panel applications, the required number of input andoutput ports are near-symmetrical and both equal to N.

A series of patents and patent applications to Lucent, NTT and Sumitomodisclose various implementations of large port count opticalcross-connects in which fiber optic connections are reconfigured by arobotic fiber handler. For example, Goossen describes a switch utilizinga circular fiber bundle and a circular ferrule loader ring in U.S. Pat.No. 6,307,983. Also, U.S. Pat. No. 5,613,021, entitled “Optical FiberSwitching Device Having One Of A Robot Mechanism And An Optical FiberLength Adjustment Unit” by Saito et al., describes the use of a roboticfiber handler to mechanically reconfigure connectors on a couplingboard. U.S. Pat. No. 5,784,515, entitled “Optical Fiber Cross ConnectionApparatus and Method” by Tamaru et al. describes a switch in whichconnectorized optical fibers are exchanged between an “arrangementboard” and a “connection board” by a mechanized fiber handler. Amotorized means of fiber payout is further described. Related approachesare described in a series of patents including JP7333530, JP2003139967,JP2005346003, JP11142674, JP11142674, JP10051815 and JP7104201.

To overcome the prior art's susceptibility to fiber entanglement,Sjolinder describes an approach to independently translate fiberconnectors along separate, linear paths in two spaced-apart planes onopposite sides of an honeycomb interface plate [“Mechanical OpticalFibre Cross Connect” (Proc. Photon. Switching, PFA4, Salt Lake City,Utah, March 1995]. In the first active switch plane, N linearlytranslating connectors are driven along spaced-apart rows by actuatorsand in the second active switch plane, an additional N linearlytranslating connectors are driven along spaced-apart columns. Row andcolumn actuators are configured perpendicular to one another.Connections are made between fiber pairs located in any row and in anycolumn by mating connectors at any of the N² common insertion pointswithin the interface plate. This approach requires at least 2N actuatorsto arbitrarily connect N inputs with N outputs.

An extension of this cross-connect approach is disclosed in U.S. Pat.No. 6,859,575 by Arol et al., U.S. Pat. No. 6,961486 by Lemoff et al.and WO2006054279A1 by J. Arol et al. They describe robotic cross-connectswitches comprised of N input optical fibers supported by N translationstages and M output fibers supported by M translation stages in asubstantially similar geometry. Each input fiber requires a shared ordedicated mechanical actuator to linearly translate both parallel to(x,y) and perpendicular to (z) the switch active planes. The connectorsrequire individual z translation to physically contact the opposingfacets of aligned input and output fibers.

The robotic cross-connect approaches described in the prior art havelimited scalability and optical performance. The application of roboticoptical switches to fiber optic patch panels demands true opticaltransparency, scalability to port counts in excess of 1000 within thefootprint of a manual patch panel, and the ability to incrementally addcircuits on an as-needed basis. In light of these limitations, wedisclose unique all-fiber cross-connect systems with superior attributesof optical transparency (low insertion loss and backreflection),scalability to large port counts (>100 to 1000's and proportional to N,the number of ports, rather than N²), high density, modularity, compactform factor, high reliability and low cost.

SUMMARY OF THE INVENTION

To meet these and other objectives we disclose in this application anautomated, remotely controllable, optical cross-connect switch systemthat exhibits near zero insertion loss, high reliability and compactsize. Further, the physical dimensions of these systems scale linearly,not geometrically (as n rather than n²) so they can readily be expandedto have capacity for thousands of fiber optic circuits. These featuresand advantages derive from a combination of unique dynamic elements andarray geometries, and also from employment of non-blocking switchalgorithms. They enable the unique optical cross-connect switchgeometries to interconnect different optical networks in an automatic,remotely accessible fashion.

In a general example of a system in accordance with the invention,programmable and robotically changeable interconnections of largenumbers (hundreds to thousands) of optical fibers, or in general anytype of flexible transmission line, are achieved by employing atwo-dimensional input array of connector terminals coupled externally toa first network. Latching optical connections can utilize long-wearingbut replaceable connector-terminal interfaces that maintain the highestlevel of optical performance and modularity. Internally the terminalsare joined by multiple interconnections within an intervening volume toa one-dimensional second array spaced apart from the first. Opticalfiber lines from the second array are coupled through buffer modules, toa second network. The multiple lines between the two arrays are mappedto follow multiple interconnecting vectors in an ordered and rule-basedfashion. Within the interconnection volume, the fibers are maintained insubstantially straight lines by modular variable length bufferssubsequent to the second array, each buffer confining a number ofoptical fiber lines and maintaining an adequate bend radius on thefibers but with capacity to retain excess fiber lengths. The buffers arescalable simply by incremental addition (typically stacking) and theoutput lines from the buffers can be connected through splice traymodules, again stackable so that more lines can be added. The arrays canalso be arranged to divide the switch volume into multiple independent,non-interfering zones, which retain their independence for arbitrary andunlimited numbers of reconfigurations. The geometries of the terminalsin the input array provide clearance for one or more robotic actuatorsto move within the interconnection volume substantially adjacent to thetwo-dimensional input array, and to be commanded by external signals tomechanically reconfigure the positions of connectors.

To reconfigure these interconnections at the first array, anon-interfering switch algorithm is disclosed, the algorithm based inpart on knowledge of the existing line vectors of the optical linesbetween the input array and the intermediate array. The algorithm canemploy either or both measurement of existing vector configurations or(more usually) stored data providing a data map of the existingconnection paths. From such stored data the system controller generatesa deterministic path dependent on and calculated from the changeablemapping of the vectorial patterns. In a particular example of a system,in accordance with the invention, motion along the path between a sourceaddress and a target address for a selected optical line is achievedboth by following vertical columnar spaces within the input array, andlaterally translating in the row direction in a manner to avoidentanglement with existing lines. In conjunction, docking ports orterminals are provided in the input array in positions which enabletemporary storage or shifting of elements so as to precludeentanglement.

The system includes an electronic processor having access to a databaseof the existing interconnection vectors, and a software program forproviding commands for the positioner to follow a deterministic paththrough the vectors of the lines in the interconnection volume. Uponreceiving a signal command for the transfer of a connector from a chosenterminal to a target terminal, the processor conducts a sequence ofcoordinated motions relative to the input array to move the connector,and its attached optical fiber line, along the two-dimensional path ofcolumns and rows, ultimately terminating at the target terminal. Thecompliance of the buffer element associated with the line beingtransferred enables variations in line length to be automaticallycompensated, without introduction of undue slackness, tensioning orbending of the optical fibers.

In a particular example of a positioner, it is mounted so as to movealong any columnar axis, fitting within the interstices of the inputarray. The positioner includes a terminal gripper at one end and athree-axis actuator at the other, so that the connector can be placedanywhere desired in the two-dimensional input array plane. In a typicaltwo-dimensional array, although other examples exist, the input array issubdivided into incrementally movable rows, each shifted by a separateactuator under commands from the controller. This allows the positionermechanism, in following deterministic rules, to shift over or under apre-existing line, by operating in a timed sequence with vertical motionof the positioner.

In a particular example in accordance with the invention, an automaticfiber optic patch-panel system comprises a two-dimensional input arrayof reconfigurable ports in a first plane, adjacent the interconnectionvolume through which optical fibers from the input array are mapped to asubstantially linear array of optical lines converging along a backboneaxis in a second plane spaced apart from the first plane. The backboneis defined by a plurality of low friction guides which converge theoptical fibers into separate paths into an adjacent buffer module, foreach set of optical lines, and the buffer module maintains thesubstantially straight path needed in the interconnection volume andcontrolled tension without excessive bending. The optical fibers exitingthe buffers can be spliced to an optical fiber cable or terminate in anoutput connector array. In one example, all buffer modules compriselow-height containers, each including a number of circular chambers forreceiving individual optical lines together with suitable stiffeningelements. In another example, the buffer may comprise a row-heightcontainer with a sufficient internal capacity for receiving a length ofoptical fiber secured at spaced apart points in a manner which allowsfor a pre-determined length of fiber to be extracted and returned undertension control.

The system incorporates numerous other features derived from itsversatility and flexibility. For example, the capability of respondingautomatically to signal commands carries with it the capability ofremote control and essentially unattended operation. Significant in thisrespect, the system includes a mini-camera mounted on the terminal endof the positioner in conjunction with the multi-functional gripper,providing a video image for both control and inspection purposes. Thissignal may be fed back to a central station to verify electronicreadouts. The video image provides a useful adjunct to the positioningsystem, in cooperation with surface indicia on the input array. Becauseposition information from the indicia can now be read by the camera,image analysis software can instruct the positioner to servo the gripperinto a precise location after the positioner has selected a coarseaddress. The gripper itself can be a spring-loaded but passive elementthat engages along a selected axis transverse to the connector, toenable it to be engaged or disengaged. Another feature in accordancewith the invention is the use of the capabilities of the system andcontroller to function as a power monitoring system with an opticalsensor integrated into the gripper, and also to monitor theinterconnection inventory. Detection of electrical conductivity betweenthe gripper and the conductive spring element coextensive with theoptical fiber is used to identity the particular fiber connector engagedby the gripper. Alternatively, ID tags are employed at connectors orterminal locations, and return signals derived from acoustic tones orelectronic readouts can thus uniquely identify the existingconfiguration of the panel.

Low loss fiber optic connections to the input plane array of connectorterminals are achieved by use of physical contact connectors insertedinto precision alignment sleeves. With replaceable, sacrificial stubelements incorporated into the alignment sleeves at the front panel, thedesign enables the extension of service life. Since near zero overallinsertion loss is desirable, the present application discloses the useof flexible fiber optic circuit structures with integral rigid springelements that oppose excessive bending. Such structures are furtherdesigned to simultaneously maintain tension along the circuit and retainslack fiber length within separate cavities.

An additional feature of this invention derives from the existence ofstatus and health-monitoring capability. In accordance with thisfeature, the system measures the optical power propagating through eachcircuit, monitors the interconnection map and confirms properoperational characteristics. Furthermore, reliable connections areachieved with single or double latching physical contact connectors,such that optical signals remain within waveguides and do not propagatein free space. The all-fiber design achieves an insertion loss of lessthan 0.5 dB and return loss greater than 50 dB for single mode fiberconnections.

BRIEF DESCRIPTION OF THE DRAWINGS

In accordance with the invention, the system and elements comprising theoptical cross-connect switch and their various combinations aredescribed in reference to the following drawings.

FIG. 1 is a block diagram of the large scale cross-connect system inaccordance with the invention;

FIG. 2 is a side, partial cutaway view of the large-scale opticalcross-connect system;

FIG. 3 illustrates a partial cutaway, perspective view detailing therobotic connector transport elements of an automated cross-connect unit;

FIG. 4A illustrates rear perspective view of a robotic gripper forengaging a fiber optic circuit connector and including an integratedcamera for precision alignment and FIG. 4B is a corresponding frontperspective view;

FIG. 5A and FIG. 5B illustrate an interior view of the array of inputterminals, with robotic gripper traveling between columns of terminalsand rows of terminals shuffling during reconfiguration;

FIG. 6A illustrates a fiber optic flexible circuit module comprised ofmultiple circuits and retractable cable units and FIG. 6B illustrates anautomated fiber end-face cleaner module;

FIG. 7A details a portion of a flexible fiber circuit element includingan integral, outer conductive stiffening member, FIG. 7B is thecorresponding cross-sectional view, FIG. 7C details a portion of aflexible fiber circuit element including an integral internal conductivestiffening member, and FIG. 7D is the corresponding cross-sectionalview;

FIG. 8 illustrates an individual fiber tensioning spool in crosssectional view (FIG. 8A) and top view (FIG. 8B);

FIG. 9A, details in partial cutaway view, a spiraled substantially woundflexible fiber circuit forming a rotary coupling interface interior totensioning spool, FIG. 9B illustrates the same in top view, FIG. 9Cdetails a spiraled substantially unwound flexible fiber circuit forminga rotary coupling interface interior to tensioning spool, and FIG. 9Dillustrates the same in top view;

FIGS. 10A and 10B detail the configuration of substantially verticallyarrayed fiber guides exiting a section of the switch backbone in end-onand perspective views, respectively;

FIGS. 11A through 11E depict protected, sacrificial and removable fiberoptic connector interfaces in various states of usage;

FIGS. 12A through 12C illustrate partial cutaway views of a doublelatching connector providing both optically transmissive andnon-transmissive operation;

FIGS. 13A and 13B illustrate the combination of union adapters withintegrated transmissive optical tap detectors, electronics and LED foruse in patch-panels having visible indicators of live traffic carryingfibers, while FIG. 13C illustrates such a patch-panel including an arrayof adapter/transmissive optical tap detector subassemblies;

FIGS. 14A and 14B illustrate an example method of fiber tensioningutilizing a passive spring element;

FIG. 15 illustrates a fiber tensioning approach utilizing an opticalfiber integral with an elastic substrate, in a retracted (FIG. 15A) andextended (FIG. 15B) configuration;

FIG. 16 is a block diagram of the automated optical cross-connect switchin communication with various transmission and test devices within atypical central office and controlled remotely from a distant networkoperations center;

FIG. 17A illustrates a connector gripper with integral electronicconnector identifier functionality and FIG. 17B details a tone detectorprobe with enhanced spatial resolution to identify individual internalinterconnections in the presence of closely spaced neighboringinterconnections;

FIG. 18 illustrates a portion of the interior side of the switch frontpanel and a system for electronically monitoring the port configurationof the switch utilizing an array of RFID tags;

FIG. 19A depicts an optical power monitoring element integrated intogripper head in which the fiber in unperturbed in FIG. 19B with no lightoutcoupling and subjected to microbend in FIG. 19C such that a fractionof light is outcoupled onto a detector;

FIG. 20 illustrates a side view of a series of parallel translationelevators for transporting connectors across the array of terminals;

FIG. 21 illustrates a partial cutaway, side view of an automatedpatch-panel system utilizing a pair of alternating robotic gripperunits;

FIG. 22A and FIG. 22B are diagrams of a braid generator with FIG. 22Arepresenting a crossing point and FIG. 22B representing a knot;

FIG. 23 is a braid diagram of a non-repeating negative braidrepresentative of a non-tangled arrangement of interconnection circuits;

FIG. 24 illustrates an arrangement of strands interconnecting a 2-Darray of ports to another spaced-apart 2-D array of ports;

FIG. 25 illustrates the spatial relationships between fiber interconnectvolume and fiber tensioning/storage volume of optical cross-connect;

FIG. 26A and FIG. 26B are perspective and top views, respectively, of anarrangement of interconnections comprised of strands followingstraight-line, shortest distance interconnections;

FIG. 27 illustrates an example trajectory to reconfigure an interconnectwhile avoiding the entanglement of strands;

FIG. 28 illustrates an example arrangement of strands exhibitingphysical interference during the reconfiguration process;

FIG. 29A and FIG. 29B are perspective and top views, respectively, of anarrangement of strands joining a reconfigurable 2-D array to a fixed 1-Darray of ports;

FIG. 30A and FIG. 30B illustrate an example of entanglement duringreconfiguration when braid characteristics are not considered;

FIG. 31A illustrates a perspective view of the interconnect volumeshowing an example trajectory to reconfigure a strand withoutentanglement, and FIGS. 31B and 31C illustrate two proper orderingconventions for circuits residing within column i.

FIG. 32A illustrates the identity braid and FIG. 32B illustrates theidentity braid in which the intermediate array has been inverted in y totwist the braid by 180 degrees;

FIGS. 33A and 33B illustrate the width of a bundle of strands at thecrossover point to determine the maximum interconnect density inaccordance with the invention;

FIG. 34A illustrates an example reconfiguration trajectory to move aninterconnect from port A to port B for positive braid ordering and FIG.34B illustrates an example reconfiguration trajectory to move aninterconnect from port A to port B for negative braid ordering;

FIG. 35A illustrates an alternate interconnection geometry, whereinstrands interconnect a 1-D array of input terminals and a 1-D array ofintermediate ports for perpendicular arrays and FIG. 35B illustrates analternate interconnection geometry, wherein strands interconnect a 1-Darray of input terminals and a 1-D array of intermediate ports forparallel arrays,

FIG. 36 illustrates an example reconfiguration path of the endpoint ofone strand undergoing reconfiguration.

DETAILED DESCRIPTION OF THE INVENTION

In this invention, we disclose all-fiber cross-connect systems 100 thatenable reconfigurable, non-blocking and optically transparent physicalconnections between fiber optic lines joining a first network to asecond network. A block diagram of the functional elements comprisingthis cross-connect system and the inter-relationships between elementsis illustrated in FIG. 1. Reconfiguration of flexible, yet taught, fiberlines are made internal to interconnect volume 108 by disengaging,translating and re-engaging fiber line connectors adjacent the internalsurface of the two-dimensional input array 170 of terminals under thecontrol of the interconnection transport mechanism 405. The interconnectvolume is bounded on the input side by the array of terminals 170 and onthe opposite side by a substantially one-dimensional array of fiberthrough-ports forming a fiber backbone 41 lying at an intermediate planewithin the cross-connect system.

The interconnect volume therebetween is populated with the intermixed,linear fiber lines. The fiber lines are suspended between arrays ofterminals 170 and ports 41 and define a three-dimensional arrangement ofvectors directed towards the one-dimensional port array 41. Behind thisintermediate port array 41, the fiber lines are individually directed toa modular arrangement of substantially identical, distributed andspaced-apart buffer elements 40. Buffer elements provide slighttensioning adequate to maintain taut fiber lines in addition toretaining excess slack in the fiber lines. The tension force produced bybuffer modules 40 on each fiber line lies substantially parallel to thevector defining the three dimensional orientation of each fiber line.

Non-interference of fiber lines within interconnect volume 108 duringarbitrary reconfiguration of any fiber line within the multiplicity ofsurrounding fiber lines is achieved when the processor 402 directspositioning controls 404 to drive the interconnection transportmechanism 405 and translate the origin of a vector associated with afiber line through the region of interconnect volume 108 immediatelyadjacent to the two dimensional input array of terminals 170. Motionproceeds in a sequential, column by column fashion such that themoveable vector endpoint weaves through the surrounding space of vectorsin a non-interfering fashion. Translation of the particular fiber lineendpoint across, up and down columns of the input array is achieved byengaging the fiber line connector body within a gripper element of theinterconnection transport mechanism 405. Carriage of fiber lineconnector is a manner which prevents entanglement of the fiber lineattached thereto is directed by electronic positioning controls 404 thatrespond to instructions generated by controller 402. The controllerexecutes multiple processes including reconfiguration algorithms 401,machine vision alignment 406, optical power measurement 409, fiberendface cleaning 408, electronic fiber circuit identification 411, andmanagement of the database of interconnections 403 in real time toaccomplish a timed sequence of elementary reconfiguration steps.

Electrical power is provided to the system through the power module 407.The cross-connect system consumes about 50 W of power primarily duringthe ˜1 minute reconfiguration time and negligible power otherwise byentering a “sleep” mode. The cross-connect apparatus can be powered notonly with traditional ac or dc power, but for remote applications, analternative is to utilize solar power or photonic power transmittedwithin fiber and with electrical storage means such as an internalbattery.

In a particular example, reconfiguration is initiated by a user orexternal software client by entering a starting point and destinationpoint for a particular fiber strand at the input terminal array which isinput to processor 402. The processor communicates with the multiplecomponents comprising the controller system 70 to direct the requiredmulti-step reconfiguration process, based in part on reading the currentdatabase of interconnection vectors 400.

In a particular interconnection transport implementation, the motion ofthe gripper while disengaging, engaging and moving the particular fiberline is synchronized with programmed individual translations of each rowcomprising the two-dimensional array of terminals 170, enabling thevector undergoing reconfiguration to maintain the proper orientationrelative to surrounding vectors such that entanglement is avoided at alltimes and for all potential reconfigurations.

A perspective view of the cross-connect system incorporating these andadditional elements is illustrated in FIG. 2, with only a subset offiber lines 21 and buffer modules 40 shown for clarity. Physicallynon-blocking automated and software-driven reconfiguration in a volumewhich scales as N, the number of fiber ports, is accomplished by linkingthe two-dimensional array of input terminals 170 with taut flexiblefiber optic circuits 21 spanning the switch's crossconnect volume 108and extending from a one-dimensional array of ports at the intermediateoptical switch backbone, 41. Contiguous fiber lines 21 pass throughordered guides at backbone 41 to self-tensioning, flexible fiber opticspools elements 42 providing automatic bend radius control and slackcable retention within stacked and modular circuits 40.

Any of the fiber circuits 21 are arbitrarily reconfigurable by engagingcircuit a selected circuit with a programmably moveable gripper 50 thatrepositions connectorized fiber optic circuits 21 within interstitialregions at the interior surface of the array of switch terminals 170.Non-interfering reconfiguration is accomplished by following anon-blocking path computed by the switch control system 70 and based onknowledge of the configuration of all intermediate lines 21 intermixedwithin the common interconnect volume 108.

This cross-connect system 100 is comprised of a combination ofindependent and separable modules to enable modularity, scalability andcustomization, including a multiplicity of stacked flexible fiber opticcircuit modules 40, an interconnection transport mechanism 405, gripper50, controller 70 and optionally a fiber end-face cleaner module 408. Atypical optical cross-connect system in accordance with this exampleoccupies a 7-foot tall, 19 or 23-inch wide rack with in excess of 1000by 1000 ports. Switch terminals 170 can be added in fixed incrementsranging between 12 to 36 (depending on the number of ports per row) byinstalling additional flexible circuit modules 40 above those previouslyinstalled modules. The output fibers 81 from modules 40 may be splicedto one or more multi-fiber cables 123 and arranged in splice trays 72,or terminated directly at the array of front panel terminals 180.

In the particular example of FIG. 2, the lower section of the switchvolume includes a reconfiguration volume 108 and the upper sectionincludes a combination of fiber splice trays 72 as well as fibersterminated in an array 180 of connectors. In general, thereconfiguration volume 108 may lie at the top, bottom, side or centralsection of the system. A central portion of the upper section is clearof obstructions to enable the robotic actuator to move, extend and parkwithin this section while being unencumbered by fibers or otherelements. The bottom-most section beneath the input terminal array 170includes a row of translatable docking ports 57 and a fixed row ofdocking ports 57′. The polished fiber endface of a connector in thevicinity of docking ports can be cleaned prior to insertion at terminalarray 170 by use of an integrated fiber endface cleaning module 408,comprising a fiber cleaning fabric ribbon in spooled form and amotorized drive unit which automatically moves the fabric relative tothe endface, thereby cleaning the fiber endfaces in a non-wearingfashion.

In accordance with this invention, the reconfigurable fiber opticconnections at the terminals of input array 170 are achieved by usingfiber optic union adapter elements which, upon insertion of opposinginternal and external fiber connectors 26, concentrically align theconnectors' polished ferrules within a precision alignment sleeve. Theselatching connectors maintain the highest level of optical performance,repeatability and reliability for a reconfigurable connection and areavailable as standard components. Low loss (<0.25 dB) and high returnloss (>55 dB) optical connections are readily achieved between singlemode fibers with cores 9 micron in diameter.

By utilizing proven interconnection elements, this cross-connect systemachieves the high possible performance. Moreover, the unique designintroduces only a single physical contact connection between any fiberof a first network and any substantially similar fiber of a secondnetwork. A wide range of standard connector styles can be incorporatedinto the switch, including standard UPC, APC, PC (simplex, duplex,multi-fiber) polish types and connector bodies based on MU, LC, SC, MT,FC, ST, Losch MD11 or expanded beam connectors. The type of latchingunion adapters 30 utilized in the input array is selected based on theparticular requirements of the application (e.g., low backreflection,highest connector density, etc.).

In a particular example, programmable switch reconfiguration is achievedwith an embedded processor 402 and software based reconfiguration andcontrol algorithms 401. This switch electronic processor may interfacewith an LCD display and keypad at the location of the cross-connectsystem to enable local push-button control and status reporting. Remoteswitch control can be accomplished by TL1, SNMP, T1V1F814, Corba,Ethernet, UART, RS-232, RS-485, USB, i2c and/or wireless control, forexample.

These control and communication elements interface with theinterconnection transport mechanism 405 to affect the non-entanglingreconfiguration of a particular fiber line. An example robotic mechanismis illustrated in partial cutaway view in FIG. 3, detailing the centralportion of the cross-connect. The array of input terminals 170 includesmultiple rows of mating receptacles, each row containing fourteenreceptacles. The number of rows is dependent upon the height of the unitand additional rows may reside outside of the mid-section detailed inFIG. 2. The output fibers are not visible here, but they typically exitthe buffer modules 40 along one of its sides. There is additionally oneor more bottom-most rows 57 comprised of docking terminals, to whichtemporary connection of fiber lines is accomplished without connectionto the first network. Docking ports facilitate reconfiguration whensurrounding terminals are occupied.

The interconnection transport mechanism 405 as illustrated in FIG. 3 isa three-axis pick-and-place actuator with a spring-loaded gripper orend-effecter 50 that interlocks a connector 26 prepared at the end of afiber line 21. Each axis of the pick-and-place unit is, for example,driven by a stepper motor for translation along a linear slide, such asa cross-roller or ball-bearing slide. Positional and end-of-travellimits are provided mechanical flags which block a phototransister lightpath and an interface which reads out the position of each axis.

FIG. 4 details an example of a multifunctional gripper 50 fortransporting a fiber line. Such a gripper may include functions such asmachine vision alignment and inspection, electrical monitoring and powermonitoring. The gripper is attached to the end of the y axis linearactuator 54 and includes a mini-camera 59 and light source 56 to captureand relay video data to processor 70 for active alignment. This videodata is processed in real time by pattern matching algorithms residingin the processor system to determine the center of mass of indiciaassociated with each connector terminal on the interior side of frontpanel and align the gripper in x and y with a selected fiber strandconnector on a frame-by-frame basis.

This gripper example utilizes metallic spring-loaded clips 51 thatengage mating cavities or depressions in the connector body 26 to retainthis connector and make electrical contact with the metallic element ofthe fiber circuit. The gripper is connected to electrical ground, forexample, so that when a fiber circuit is attached to gripper, anelectrical circuit is completed and used to trigger subsequent moves.Alternatively, the connector may be held within a formed orstamped-metal retaining clip, the clip including locking features torigidly hold connector, including attachment feature(s) to which thegripper engages and conductive features to make electrical contact withconnector. The gripper body is provided with radiused exterior surfacesto prevent excessive bending of surrounding fiber strands, which maycome in contact with the gripper during reconfiguration.

The gripper 50 engages a particular connector by lowering itself ontothe connector body 26. Subsequent translation of the gripper along thelongitudinal axis of the connector is adequate to extract or insert theconnector 26 from or into its mating receptacle at the interior side ofthe front panel terminal array 170. Conversely, the fiber connector isdisengaged from the gripper by raising gripper (in y) after theconnector is translated along the longitudinal axis (z) of connector tomechanically latch within the mating terminal on the front panel array170.

In a particular embodiment shown in partial view in FIG. 5A, the innersurface of the optical cross-connect switch's 100 front panel ispopulated with a substantially regular arrangement of connectorterminals 170 comprised of union adapters 30 mounted to independentlymoveable panels 46 to which patchcords originating from transmission andtest equipment are inserted at the opposite, outer surface (not visiblefrom this perspective). For clarity, only one flexible fiber opticcircuit 21 inserted into union adapter 30 is illustrated. In thisparticular example, the array of spaced-apart input terminals 170 arearranged in a series of 10 independent rows with 14 columns each,wherein each row is able to independently translate between threepositions in the direction of row axis 58. One or more additionaltranslatable rows 57 of docking ports 39 is provided. These ports may besituated below the bottom most row of input terminal array 170 as shownhere, or may be placed at an intermediate row within the stack.

The non-interfering translation of a particular fiber optic circuit 21between this array of input terminals 170 is accomplished at relativelyhigh speeds (˜1 minute) by the coordinated movement of the gripper 50 upand down the columns and independent shuffling of each row of inputconnectors 30 by a half column spacing in one of three positionsparallel to the x axis 58.

While this example illustrates a cross-connect apparatus fully loadedwith flexible circuit modules 40, in general, the switch may bepartially populated to provide spare capacity. Fiber lines are added byfirst parking the gripper and robotics outside of the fiber interconnectvolume. Immediately thereafter, flexible circuit modules 40 may be addedon a row-by-row basis by stacking modules above the previously installedcircuit modules 40. Alternatively, if a circuit module at anintermediate location within the stack is to be replaced, the circuitsattached to the corresponding front panel row may be moved to the row oftemporary docking ports and those circuits originating from the flexiblecircuit modules may be returned to its corresponding front panel row.

Once this is complete, the entire module may be removed, enabling theupper circuit modules 40 to be lowered one position to fill the gap andallowing a replacement circuit module to be added at the top of thestack. Fiber connections to this new module are completed by exchangingthe temporary input connections made at docking terminals with thereplacement module terminals and routing the outputs of the circuitmodules to either the output port array 180 or splice trays.

Reconfiguration Procedure

The reconfiguration of fiber lines within the cross-connect requirescoordinated and timed motion of various elements to prevententanglement. Initially, the gripper 50 is extended above the activeswitch volume 108 and each row of input terminals is in horizontalalignment (FIG. 5A). Reconfiguration of a particular flexible circuit 21is accomplished by a column by column sequence of translations, eachcomprised of a series of vertical (y) and horizontal (x,z) translationsof gripper 50 and coordinated shuffling of input rows 46 by +/−half acolumn spacing parallel to the x axis 58, and by the movement of gripper50 into one of the free columnar zones created by such shuffling (FIG.5B). Fine positioning of gripper 50 relative to terminal receptacles 39is achieved by a vision alignment system utilizing the gripper camera's59 video signal, in which the center of indicia 137 located adjacenteach terminal are identified within a video frame by pattern matchingalgorithms to stored images of indicia under similar lightingconditions. The indicia 137 center is tracked in real time as a feedbacksignal corrects the position of the gripper 50, such that the fiberconnector 26 attached thereto is precisely aligned and inserted intoterminal receptacle 39.

In addition, unique input port identifiers 139, either a barcode ornumeric identifier printed on (e.g., screen printed, pad printed, lasermarked or engraved) or attached to (e.g., a printed label) the interiorsurface of each row, can be read by an optical character recognition(OCR) or barcode reading algorithm using the images provided by thegripper camera 59 to automatically determine the value of the uniqueidentifiers 139, and use this value to unambiguously determine, eitherdirectly or through a look-up table procedure, the location of thegripper within the interstitial gap of the columns of connectors. Thisenables the cross-connect controller 70 to re-establish positionalbearings and resume the reconfiguration process, should it beinterrupted by a potential failure of power, software or hardware.

Rows are displaced with a polarity that prevents physical interferenceof surrounding fiber lines with moving fiber line 21. The polarity ofeach row's shift is dictated by control algorithms to ensure that anyparticular circuit 21 travels below those intervening circuitsoriginating from a higher level and above all those intervening circuitsoriginating from a lower level. In general, shuffling rearrangementoccurs each time the connector 26 passes to the next column, either overthe top-most row 76 or below the bottom-most row 75 of input terminalarray 170. Movement of each row 46 is actuated by one or more solenoids,linear actuators 47, or a combination thereof.

In a particular example, the gripper 50 prepares to disengage a softwareselectable fiber circuit 21 first by initial coarse alignment utilizingcontrol of stepper motor counts relative to optical limit and/or homeswitches, followed by a servo alignment based on gripper mini-camerafeedback and pattern matching to indicia referencing the position ofeach terminal receptacle 30 within the input array 170. Once the gripperis in alignment in x and y, it is lowered a fixed distance tomechanically engage the target connector body 26 and withdrawn in z withsufficient force to pull the mechanically latching connector out of itsmating receptacle.

In one scenario, the connector 26 retained by gripper is then translateddown the column and, utilizing a similar pattern matching alignmenttechnique, the connector is inserted into docking port 39 residing atthe bottom most row 57 of the switch. The gripper 50, utilizing passivespring engagement element(s), is only able to engage the connector bodyby downward, vertical approach and only able to disengage the connectorbody by upward, vertical approach. Therefore, the gripper 50 releasesthe connector 26 presently retained in an input terminal receptacle byascending back up the column to the top of active switch volume 108 todisengage the latching mechanism between the gripper and connector. Thegripper then travels parallel to the row axis 58 to the nextintermediate column located between the initial column and thedestination column.

The above process is potentially repeated for each intermediate column.The gripper 50 descends into the first intermediate column, disengagesthe connector 26 from the docking receptacle 39, and ascends up and outof this column with the connector and flexible circuit 21 attachedthereto. The gripper 50 then translates parallel to the rows to a secondintermediate column located between the first intermediate column andthe destination column. The rows shuffle once again according to theparticular port mapping, and the gripper 50 with connector 26 descendsinto the column and inserts the connector into a different bottom-mostdocking port 39′. The process continues in a similar fashion until theconnector 26 and fiber line 21 have passed through each column ofterminals, or zones, to reach its destination. The end of theinterconnect line typically follows a weaving trajectory through theneighboring lines to prevent entanglement.

In a further example, the fiber end-face of connectors may beautomatically processed by cleaning module 408 during the switchingcycle to ensure repeated low-loss fiber optic connections free ofcontaminants on the delicate end-face. The cleaning system utilizesconsumable cleaning fabric on spools, pressurized air, ultrasound and/orwet chemical means.

In a particular embodiment (FIG. 6B), cleaning fabric is provided in atape form 84 and retained on spool cartridges 83-1, 83-2 within aslide-in tray module 82 located below the bottom-most row of the inputterminal array 170. Dispensing of unused cleaning tape is controlled bymotor(s) 86-1 and 86-2. Once cleaning tape is consumed, cleaning module408 can translate out of switch along slide 87 to eject used cleaningcartridges and insert replacement tape. Cleaning of connector 26 isachieved by contacting fiber endface to tape 84 supported by elastomericbacking 85 and by relative movement of endface relative to tape.

Flexible Circuit Modules

Modularity is achieved by adding multi-fiber circuit modules 40 on arow-by-row basis above those already installed to the lower portion ofcross-connect. The footprint of the cross-connect is independent of thenumber of ports within limits. In a particular embodiment, the flexiblecircuit modules 40 include a corresponding row 46 of the input connectorarray 170 with its multiplicity of flexible circuits 21 pre-attachedthereto for ease of installation. The installation of additionalcircuits then requires a relatively simple process in which the actuator54 and gripper 50 is fully extended above switch volume 108, so that oneor more circuit modules 40 including translatable front plates 46holding connectors 30 can be installed by sliding in from the rear ofthe switch 120.

Physical interference between flexible circuit elements 21 is eliminatedby moving the connector 26 along a deterministic trajectory based on thelocations of all intervening circuit elements 21. Moreover, it is alsonecessary that the flexible fiber circuits 21 within the switch volume108 follow a substantially linear path under slight tension to preventphysical interference with other circuits. The multiplicity of flexiblefiber optic circuits 21 attached to the input connector array 170 passthrough low friction, strain relieving spacing guides 45 extending fromswitch backbone 41 to an arrangement of fiber take-up spools 42 adjacentto the switch backbone 41 and disposed in a substantially modulararrangement. Spools 42 retain excess fiber optic cable lengths whilemaintaining greater than a minimum radius of curvature and maintaining aslight tension on the flexible fiber optic circuits 21 within theinterconnect volume 108.

In a particular embodiment illustrated in top view in FIG. 6A, anarrangement of spools 42 for fiber retention reside in circular pocketson a common substrate 44 and guides 45 for fiber circuits 21 pass therebetween. Retraction of any particular flexible circuit 21 isaccomplished by an internal power spring within each spool, whichtransfers torque to the take-up spool 42 and maintains a requiredtension value on the spring-reinforced fiber optic circuit 21. In analternate embodiment, rotation of the take-up spool 42 is achieved by amotorized means using a shared retraction motor drive unit and clutchmechanism to transfer a torque to each spool. Such tensioning reducesslack cable within the interconnect volume.

The fiber circuits 21 extend under slight tension from the take-upspools 42, thereby releasing only the circuit length required for theparticular circuit to follow a substantially linear path between switchbackbone 41 and the two-dimensional array of interface ports 170, whileretaining excess length on spool 42. The required length of extendedfiber circuit 21 depends on the location of the fiber's termination atthe front plane as well as the particular circuit location at the switchbackbone 41. The length of flexible fiber optic circuit 21 is typically0.25 to 3 meters for a 1000 port switch.

In a particular example, eighteen retractable fiber optic spools 42 aredistributed across the rear portion of circuit module 40. The circuitmodule is low profile with a typical height of 18.0 mm, width of 500.0mm and depth of 750.0 mm. The spools have a typical outer diameter of25.0 to 90.0 mm. Eighteen independent flexible fiber optic circuits 21extend from spools into the branching low friction fiber guides 45. Theguides 45 route flexible circuits 21 from the spools 42 to a segment ofthe switch backbone 41 and are fabricated, for example, of Teflon (PTFE)or other low surface friction tubes (e.g., polyethylene, PFA) or byinjection molded guides coated with a suitable low friction film.

Selected fiber outputs 81 can potentially be connected to other fiberoutputs 81 by splicing, for example. This enables input ports to beconnected to other input ports as well as connected to output ports bylooping back the outputs. Similarly, input ports can be connectedthrough external jumper cables so that output ports can be connected toother output ports as well.

In an additional example, fiber outputs 81 may be connected to fiberoptic splitters such as 1×2, 1×16 or 1×32 splitters that are integratedwithin the circuit module 40. The multiple fiber outputs can convergeinto a single output by configuring the system with fiber opticcombiners; alternately, the fiber outputs can be further split toproduce additional outputs. For example, outputs can be duplicated byincorporating 1×2 splitters to offer a protection circuit path. In analternate example, a single feeder fiber can be attached to a fiberoutput of an automated cross-connect within a fiber distribution hub.The fiber output is then split into, say, 16 outputs by a passive fiberoptic splitter within the circuit module 40. The 16 outputs can theninterconnected to any terminals of the input connector array 170. Thisimplementation is particularly valuable for remote fiber distributionhubs in passive optical networks. The cross-connect outputs or inputscan additionally be provided with fast 1×2 switches to offer switchableprotection circuits paths for fast service restoration. Thermo-opticswitches, for example, provide sub-ms switching times.

Flexible Circuit Elements

In a further aspect of this invention, we disclose flexible fiber opticcircuit structures 21 comprised of one or more optical fiber elements 20and one or more spring elements 23 longitudinally adjacent to oneanother and arranged in a fashion that prevents excessive bending of theoptical fiber elements 20 when the flexible circuit 21 is tensioned. Ina particular embodiment (FIG. 7A), the flexible fiber circuit 21 iscomprised of a acrylate coated, loose tube or tight buffer optical fiber20 loosely wound with a straight segment of spring wire 23 or passingthrough the center of a loosely spiraled stainless steel spring 23′. Theforming of the steel spring 23′ into a loose spiral with an innerdiameter of 1 mm and a longitudinal spacing per turn of about 50 mmretains the central optical fiber and provides stiffness and strainrelief while minimizing the potential for micro-bends within the opticalfiber 20. The typical spring wire diameter is 0.010 to 0.015 and thespring material undergoes a spring-temper or hard-temper process toincrease its yield stress. Typical optical fiber 20 outer diameters,including a buffer or loose tube, are 0.25 to 1.5 mm.

In the example for which the spring element 23′ is external to jacketedfiber 20, the spring element 23′ is advantageously coated with a lowfriction fluoropolymer (e.g., PTFE) or polymer film 25 to facilitate thelongitudinal sliding of spring element 23′ relative fiber element 20,and also to facilitate the sliding of flexible circuit 21 relative toother flexible circuits. Moreover, the film 25 provides an electricallyinsulating jacket that prevents electrical contact between adjacentflexible circuit elements 21. The jacket may be selectively stripped incertain regions of the wire to expose the conductor and enableelectrical contact. These electrical elements are advantageous inseveral implementations of electronic port identification as describedin later sections. The spring 23′ and fiber 20 elements may be attachedat one or more spaced-apart locations along the length of the flexiblecircuit 21. It is advantageous that the spring element 23′ experiencesthe tension and fiber element 20, being slightly longer in length, notbe subjected to a tensile force.

In a further aspect of the invention (FIG. 7B), both the spring 23 andoptical fiber 20 are retained within a common loose tube sleeve 24 whoseinner diameter is sized to accept one or more spring elements 23 and oneor more fiber elements 20. Suitable materials for the sleeve 24 includematerials with low surface friction characteristics such asfluoropolymers (i.e., PTFE) with inner diameter of 0.600 mm to 0.750 mmand outer diameter of 0.9 to 1.0 mm. Thick-walled tubing itself canserve as a stiffening element, potentially obviating the need for aportion of or the entire metal spring element. Typical acrylate orpolyimide coated silica optical fiber 20 is 0.250 mm in diameter andspring element 23 is 0.250 mm diameter spring tempered steel wire.

In a particular example, flexible fiber optic circuits 21 utilizeoptical fibers 20 which are coated, buffered or within a loosetube/tight buffer and longitudinally adjacent to an elastic stiffeningelement 23 which maintains a minimum bend radius throughout the range ofmotion occurring during fiber circuit reconfiguration.

In a further example, the optical fiber 20 with a waveguide core isloosely twisted about a wire spring 23 of spring-tempered orhard-tempered stainless steel, with about 1 full twist per 2-10 cm. Thetypical wire diameter is 0.250 to 0.350 mm and the typical fiberdiameter is 0.6 to 0.9 mm for tight-buffered or loose-tube fiber.

In an alternate example, optical fiber circuits 21 are intermittentlyattached to spring 23. Typical spacing between attachment points is 5cm. Adhesive may be in the form of self-adhesive die cut shapes orprecisely dispensed adhesive drops. As the fiber circuit isreconfigured, the fiber 20 and spring 23 are free to separate whilemaintaining at least a minimum local radius of curvature on the opticalfiber.

In an alternate example, a loose tube buffer sleeve 24 surrounding theoptical fiber 20 and wire spring 23 will allow the spring and fiber tofreely piston within the tube's lumen as the combined element isreconfigured. The spring is attached to connector body 26 at theproximal end and the fiber and spring are free to longitudinally slidewithin the buffer tube. The buffer tube may be 0.5 to 0.9 mm in diameterand fabricated of hytrel or fluoropolymer such as PTFE (Teflon), forexample.

In a further example, the flexible fiber optic circuit may include alongitudinally varying stiffening element that provides variation instiffness along the circuit. In a particular implementation, a smalldiameter (e.g., 250 microns) stiffening member runs along the entirelength of the fiber and an additional stiffening member (e.g., 350micron diameter) augments the stiffness at the proximal end of thecircuit. Alternatively, a wire element with longitudinal variations indiameter may be utilized.

In these examples, the flexible fiber optic circuit follows asubstantially linear path. This path of circuit 21 is comprised of astraight-line segment and includes spaced-apart arc segments of limitedlength with greater than a minimum bend radius at the terminal array andat the intermediate port array (as shown in FIG. 14A, for example).

Take-Up Spools for Slack Retention

In a further aspect of the invention (FIG. 8), slack fiber managementand fiber tensioning are provided by rotating take-up spools 42. Theproximal end of fiber circuit 21 is terminated in connector body 26attached to a port 30 of input terminal array 170. The intermediatesection of circuit 21 behind the fiber backbone 41 is wound onto amandrel section 96 of rotating spool 42 with a diameter greater than 25mm or the minimum bend radius of the particular fiber. The fiber exitsthe spool section and follows a transition channel 48 through mandrelwall 96 within spool element to enter a rotary interface 90 fibercircuit segment comprised of a multiple turns of fiber circuit 21 abouta mandrel feature 99 extending from bottom side of spool 42. Theflexible circuit 21 or equivalently, the composite optical fiber/springstructure, thereby maintains a substantially multilayer spiralarrangement constrained within an annular cavity bounded at its innerdiameter by the annular mandrel wall 99, whose radius is greater thanthe minimum bend radius of optical fiber 20, and bounded along the outerdiameter by a circular wall 94 extending from the base 44 of module 40.As the spool 42 rotates, the average winding diameter of flexiblecircuit 21′ within the annular cavity 95 either decreases or increases.

This low profile, retractable fiber optic device 210 therefore retainsexcess lengths of flexible fiber optic circuits 21 on a spool 42 whichis free to undergo a limited number of rotations, the number limited bythe length of the spiraled flexible circuit 21 within the all-fiberrotary interface 90. Such retractable devices 210 have been previouslydisclosed by Kewitsch in U.S. Pat. No. 7,315,681, entitled “Fiber opticrotary coupling and devices”. The retractable device comprises a take-upspool 42 including a first mandrel wall 96 about which the flexiblecircuit 21 is wound, an annular rotary interface cavity 95 thataccommodates a finite number of rotations of the spool 42, and a centralpower spring 91 attached to inner shaft 92 to transfer torque onto thespool, thereby tensioning the fiber. In an alternate embodiment, thefiber take-up spool 42 is powered by a motor unit.

FIG. 9 schematically details in cross section the rotary interfaceportion 90 of the retraction device 210 in the fully wound (9A) andunwound (9B) configurations. This drawing illustrates a structure whichcouples fiber between the rotating take-up spool and the fixed circuitmodule 40 without stressing the fiber circuit. This structure is similarto a coiled spring of extended height along an axis of rotation with anoptical fiber further coiled longitudinally about the spring element,where one end of spring is free to rotate relative to the other end ofspring. In the fully wound configuration, the flexible circuit section21′ accumulates in the vicinity of the inner diameter 99 and in thefully unwound configuration the same flexible circuit section 21′accumulates along the outer diameter 94. The annular volume provided forthe flexible circuit segment 21′ is adequate to allow this spiralsegment to wind and unwind under a finite number of rotations of thetake-up spool 42, while subjecting the internal optical fiber 20 tominimal bending stress as it is carried by spring element. The take-upspool 42 is typically able to undergo 5 to 10 full rotations. Theproximal end of circuit segment 21″ is attached to rotating spool 42,about which a variable length of circuit segment 21 winds. The distalend of the flexible fiber optic circuit 21′″ exits at the outer diameterof the rotary interface 90, is fixed in length and routed to appropriatefixed output ports as an individual fiber optic element 20. In aparticular example, the spring element 23 is separated from the fiberelement 20 at some location before the distal end of circuit 21 forconnection to electronic monitoring circuitry. The torque to rotate thetake-up spool about mandrel 92 is provided by a power spring 91 or bythe spring element associated with the fiber circuit 21.

The length of the wound circuit element 21′ within rotary interface 90is of fixed length between 0.5 and 6 meters. The distal end of circuit21′″ is fixed in length (typically 2 meters) and fixedly routed toeither an output port connector 30 or splice tray 72.

In a further aspect of the invention, the centers of flexible circuits21 pass through conduits 45, which lie at or in the vicinity of thecenterline of the switch backbone 41 segment of flexible circuit module40. FIGS. 10A and 10B detail a portion of the backbone with the flexibleconduits 45 extending there from. The flexible conduits 45 further serveas strain relief and prevent excessive bending of the circuit elements21-1, 21-2, . . . that pass through as they exit the rigid backbone 41.The flexible conduits 45 will partially bend to provide a gradualtransition to the nominally straight-line paths of the flexible circuits21 within switch interconnect volume 108. Typical inner diameters of theflexible conduits 45 are in the range of 1.2 to 2.0 mm with a wallthickness of 0.125 to 0.500 mm.

High-Reliability Optical Connections

The optical performance of the automated patch-panel in accordance withthe invention is equivalent to the highest performance possible formanual patch-panels because the optical fiber is interrupted by only asingle connector interface 30 per port. In contrast, switch technologiesof the prior art require additional connector interfaces per port tofacilitate interconnection to external patch cords. The connectorinterfaces 30 utilized herein provides low loss and low back reflectionby passive alignment of optical fibers terminated in polished ferruleswith precise fiber optic core concentricity. The fiber-ferrule end facesare polished according to APC (angled physical contact), UPC(ultra-physical contact) or PC (physical contact) standards. Opposingfibers are mated by inserting the polished ferrules into opposite endsof a precision split sleeve until they touch. The compliant split sleeveachieves precise core alignment of the waveguide cores within the fiber.Physical contact connectors with ceramic split sleeves, under idealconditions, have lifetimes exceeding 1000 to 5000 re-matings. The use ofceramic rather than metallic split sleeves helps to prevent abrasion andformation of free particulates during repeated insertion.

Physical contact connectors, by virtue of the optical contact betweenradiused ferrule end faces and wear on the connector and adapterhousings, can begin to degrade after 1000's of mating cycles. Thedurability can be substantially increased by maintaining a high level ofcleanliness within the switch volume, providing automatic fiber end-facecleaning capabilities and by reducing particulate shedding duringinsertion of the connector by utilizing mating receptacles with ceramicsleeves and potentially metal housings. High optical performance for anessentially unlimited number of switching cycles (e.g., >1,000,000mating cycles per port) is achieved by use of the field-replaceableprotective connector cartridges 35 with lifetimes of >500mating/demating cycles per cartridge, and by the use of front panelunion adapters 30 that include internal fiber stubs. The design and useof such protective fiber optic union adapters 30 and male-to-femaleconnector cartridges 35 have been previously disclosed in U.S. patentapplication Ser. Nos. 11/865,731 and 11/307,688 filed by Kewitsch. Thenumber of re-connection cycles per port is optionally stored withinmemory to alert the user to replace a particular protective connectorcartridge 35 and/or union adapter 30.

Disposable connector interface units 30 and 35 reduce the up-front costand complexity of optical switches while achieving optical connectivityperformance equivalent to that of standard manual patch panels. Typicaloptical loss is <0.25 dB because only one connection (those front panelports 170) per circuit is required and the typical return loss is >50dB. The patch panel connector interfaces 30 utilize PC, UPC or APCterminations and MU, LC, SC, MTRJ and/or MPO style connectors.

FIGS. 11A through 11E illustrate the protective male-to-female interfaceadapter 35 and union adapter 30 under various cross-connect installationconditions. FIG. 11A is an exploded view of the connector 26, adapter 35and union 30 attached to a front panel 46. The adapter 35 includes aninternal fiber stub/ferrule 28′ that physically isolates the flexiblecircuit's 21 connector 26 from repeated mating as the switch isreconfigured. This sacrificial adapter element 35 prevents damage to thepolished ferrule tip 28 of connector 26. The ferrule tip 28 ofprotective adapter 35 experiences wear-out and can be replaced from thefront panel 46 of the cross-connect switch 100.

After installation of a connector receptacle (FIG. 11C), thespring-clips 34 on connector receptacle 30 firmly engage the receptacleto the front panel 46. When the receptacle 30 requires replacement, thereceptacle is removed from its cutout in the front panel (FIG. 11E).During this replacement procedure it is necessary to maintaincleanliness within the internal switching volume 108. This can bemaintained by providing a fan with a high efficiency particulate filter(HEPA) 250 to produce a slight positive pressure inside the switchinterconnect volume 108 during the connector replacement.

In a further aspect of the invention, it is of potential value that eachport of the cross-connect switch 100 have a non-transmissive state (>30dB loss) in addition to the transmissive state (<0.5 dB loss). In aparticular example, this is accomplished by providing a number ofdocking ports 39 equal to the number of input terminals 30, to whichcircuits may be physically attached while remaining opticallydisconnected. Alternately, there are advantages in providing thisfunctionality in a fiber optic union adapter 30″ which provides twolatched mechanical states when interfaced with standard fiber opticconnectors 26, such as the SC, LC and MU types. For example, as theconnector 26 (FIG. 12A) is longitudinally inserted into the unionadapter 30″ and first engages the latch 29 (FIG. 12B), it enters a firstmechanically latching state corresponding to a non-transmissive oroptically disconnected state. This state is characterized by an air gap136 between the opposed ferrules 128 which produces a substantialinsertion loss (>30 dB). By inserting the connector 26 further in thelongitudinal direction (FIG. 12C), the connector 26 enters a secondmechanically latching state corresponding to a transmissive or opticallyconnected state, in which the opposed ferrules 28 are physicallycontacted for low loss.

In an additional embodiment of this invention, a fiber optic adaptersubassembly 61, with integrated optical power monitoring, such as thosedisclosed in U.S. Pat. No. 7,289,197 to Kewitsch, may be utilized ateither the input or output array of terminals to monitor the opticalpower passing through each port (FIG. 13). This type of optical detectorutilizes a patterned transmissive film such as ITO formed on thepolished endface 28″ of a fiber stub, for example, the resistance ofwhich is measured by electronics 62. The optical power readings areconverted to electrical signals from these adapters that may beinterfaced with controller 70 by way of electrical interconnections 69and/or used to activate light emitting diodes 63 (LED's) adjacent theconnector receptacle. The state of the LED indicates whether the opticalfiber attached to receptacle 30 is carrying live traffic or is dark.

These LED signals, or live-fiber indicator lights, help to preventtechnicians from erroneously removing those fiber optic patchcordscarrying live traffic from among the multiplicity of surrounding fiberoptic cables (not shown here for clarity) attached to the front ofpatch-panel 79. This live-fiber indicator feature ensures that upondisconnect of a fiber, network operations are not compromised, opticaldamage to the polished fiber endface of disengaged connectors isprevented, and potential safety hazards associated with the opticalpower escaping from the end of a live fiber is mitigated.

Example: Multilayer Flexible Circuit Structures

In a further example (FIGS. 14A and 14B), the flexible fiber opticcircuit line 21 is attached behind the backbone 41 and within thecircuit module 40 to a substantially non-parallel second spring element23-3 whose stiffness is substantially greater than spring element 23within circuit 21. Attachment is achieved by use of adhesive attachmentelements 141 and 142, such as self-adhesive Teflon film. When theproximal end of circuit 21 is fully extended to reach the most distantport located at 170-1, the second spring element 23-1 is bent to itsminimum radius of curvature to produce the largest tension force oncircuit 21. This tension force is by design adequate to retract thecircuit 21 while not being excessive as to over bend the circuit 21 atlocations 170-1 and 170-2. To enable electrical traceability of theflexible fiber circuits, the spring element 23 is terminated in anelectrical terminal block 129 to interface with switch control system 70electronics.

In a particular example, spring elements 23, 23-1 are fabricated ofspring tempered stainless steel and/or carbon steel. Interleaved withspring elements is a low surface friction separation film, such as0.002-inch thick PTFE material. This film provides not only low frictionbut also separates the multiple flexible circuits so that they can moveindependently. This film is also of sufficiently light weight that thestack of such film does not add sufficient weight on top of the bottommost layer and prevent free motion of the bottom most flexible circuit.More specifically, five layers of substantially planar flexiblecircuits, each surrounded on top and bottom by sheets of low surfacefriction film, form a vertical stack wherein vertical support of thecircuits by a rigid metal or plastic tray (e.g., 0.025 thick aluminum)is provided approximately every five layers to prevent collapse andinterference of the multiple layers under gravity.

In a further aspect of the invention (FIG. 15), the retraction force maybe provided by a flexible, elastic substrate 114 to which the fiber 20is attached. By pulling on one end of flexible substrate 114, its lengthis increased, thereby stretching or partially unfolding the path offiber 20′ on deformed substrate 114′ in a manner that produces at leasta minimum bend radius. Suitable materials for the flexible substrate 114include thin rubber or nylon sheets or woven structures exhibiting highelasticity and low creep.

In an additional aspect of the invention, the retraction force may beprovided by a coiled extension spring structure, to which the fiber isintermittently attached, such that the optical fiber follows a pathexhibiting greater than its minimum radius of curvature.

Example: Automated Patch-Panels in Telecommunications Central Office

In accordance with the invention, the automated fiber optic patch-panelsystem 100 disclosed herein enables a remote Network Operations Centerin city A with network management systems and software 270 to control adistant patch-panel in city B through its controller 70 attached tonetwork interface 277 (FIG. 16). The patch-panel, attached to a secondnetwork through trunk cable 123, enables test equipment 271 such asoptical time domain reflectometers (OTDRs), bit error rate testers(BERTs), and optical spectrum analyzers (OSAs) to be connected to thepatch-panel using static patch cords 275, and thereby share testequipment among the many optical links serviced by patch-panel. Inaddition, network transmission equipment 273 from a first network, suchas wavelength division multiplexers (WDMs), reconfigurable opticaladd/drop multiplexers (ROADMs), Erbium doped fiber amplifiers (EDFAs)and channel monitors are patched-in to the input ports of the automatedpatch-panel. This enables the network to be remotely reconfigured andtested by the network management system software 270.

Example: Internal Electronic Status Monitoring and Error Reporting

In accordance with this invention, the reconfiguration of the opticalcross-connect switch first requires knowledge of the positions of allconnectors 30 of flexible fiber optic elements 21 at connector array170. The mapping can be based on switch port maps stored in a databasein the memory of controller 70. The mapping is continually updated asthe switch ports are reconfigured. An automated fiber optic patch-panel100 in accordance with the invention may include electrical tracingelements within flexible fiber optic circuits 21 to trace the locationof each flexible circuit 21 across the array of ports 170. For example,an electrical voltage signal is launched down at least one of theflexible optical circuit elements 21 by making direct or indirectelectrical connection to a conductive element, for example, theconductive spring member 23 within the flexible optical circuit 21.

In a particular aspect of the invention, the gripper 50 makes directelectrical contact with fiber element 21 when the gripper engages theconnector body 26 (FIG. 17A). A continuity tester 77 switched to theconductive element 23 of any fiber circuit 21 by use of circuitmultiplexer 78 ascertains which fiber element is attached to which inputterminal 30 of array 170. The techniques of continuity testing andvoltage tone tracing may utilize one or two conductors per fiber opticcircuit 21. Continuity is established with only one conductor per fiberif a common return path is provided. In the voltage mode of tone tracing(in contrast to current mode), a radio frequency or audible frequencyvoltage tone is sent down one conductor and the ground reference isprovided by a common ground, such as shielding and/or enclosures.

More particularly, to determine fiber connections based on a continuitytest, the gripper 50 makes physical and electrical contact with aparticular connector 26 and its electrically conductive element. Bymeasuring the resistance between the other end of the fiber circuit andthe gripper, the identity of the circuit and whether it is engaged ordisengaged from the gripper may be determined. A voltage may be appliedto each conductive element 23 of fiber circuit 21 of the cross-connectin a sequential fashion, by electrically switching between conductiveelements 23. By repeating this process for all ports, the entire portmapping can be ascertained.

In an alternate embodiment, flexible circuit 21 elements include thespring element 23 located outside of the optical fiber's 20 sleeve, andthe electrical insulation layer 25 on spring element 23 in vicinity ofconnector body 26 is removed. This enables a direct electrical contactand continuity test to be made between the gripper 50 and the particularflexible fiber optic circuit 21 being electrically contacted.

Alternatively, the fiber optic circuit element 21 is individually andindependently excited by a voltage or current tone produced by a tonegenerator 64 interfaced with controller 70 (FIG. 17B). Such tones may besinusoidal in nature and lie within the frequency range of kHz to MHz,typically 1 to 10 kHz, to facilitate a wireless determination of theconfiguration of optical circuits 21. Back-end termination points at thedistal ends of flexible fiber optic circuit elements 21, located throughthe switch backbone 41 and beyond the exit point from flexible opticalcircuit stack 40, are attached to independent electrical conductorswhich interface to an electronic switch matrix and tone generator 64. Aunique voltage tone may then be switched onto any one of the particularcircuits 21.

Alternately, the gripper may further include a voltage probe 65 (FIG.17B). By positioning the gripper 50 in the vicinity of any connector 26,the controller 70 directs the tone generator 64 to launch a tone downeach conductive element 23 of fiber circuit 21 of the cross-connect in asequential fashion, by electrically switching between conductiveelements 23 excited by the tone generator 64. By repeating this processfor all ports, the port configuration can be ascertained.

The voltage probe 65 must have sufficient spatial resolution tounambiguously identify which connector 26 is attached to the particularport under test in the presence of closely spaced neighboringconnectors. For the voltage probe design of FIG. 17B, the flexiblecircuit 21 under test is partially inserted into the voltage probe unitsuch that it passes through a slot within the ground plane 22′. Theground plane 22′ localizes the electromagnetic radiation which isdetected by the voltage probe's antenna. The ground plane is attached toboth the voltage tone detector circuit 68 and the voltage tone generatorcircuit 64 by way of a common ground wire 22. The voltage tone generatorcircuit 64 is attached to the flexible circuit's 21 conductor element 20to excite the particular circuit 21 with a voltage tone.

In a further example, an electrical voltage tone is launched down any ofthe flexible optical circuit elements 21 by making direct or indirectelectrical connection to the conductive element, for example the springmember(s) 23 within the flexible optical circuit 21. Thereby, thecircuit element is individually and independently excited by a voltageor current tone produced by the tone generator. The tone generatorfunctionality may be incorporated into the reader 615 or may be aseparate module. Such tones are oscillatory in form and lie within thefrequency range of kHz to MHz, typically 1 to 100 kHz. A unique voltagetone may be switched onto any one of the particular fiber optic elements23, the frequency and amplitude of which are detected by an array ofantennas 67 distributed among the two-dimensional array of ports 30.

In a further example, the gripper 50 includes a downward directed lightsource and photodetector or camera to check for the presence of anyimproperly placed fiber optic circuits 21 within the column or zone 101.This collision avoidance feature would then provide an alert and a faultindicator. In this fashion, proper operating characteristics can beconfirmed during the lifetime of the switch.

Example: RFID Port Monitoring

In a further example (FIG. 18), each flexible fiber optic element 21 isassociated with a unique RFID identifier tag 66 whose physical locationmay be ascertained by electrically scanning the two-dimensional array170 of connectors 26. For example, this identifier may be in the form ofa radio frequency identification (RFID) tag 66 with a unique serialnumber. The RFID tag 66 is attached to each flexible fiber optic circuit21 in the vicinity of the fiber optic connector body 26. Each tag 66includes a unique identifier associated with a particular fiber opticswitch port through a port map, which is stored in memory. When theconnector 26 is attached to a particular connector receptacle/port 30,its tag produces the strongest electronic signature when read by the setof electrodes 619, 617 which locally encircle the particular receptacle30 to which it is attached. Particular pairs of electrodes whichtransmit the RF excitation and tag read signal are sequentially excitedby an electrical multiplexer attached to tag reader circuit 615.Electrodes are patterned on a flexible electrical circuit 611, forexample, formed on a polyimide film and connected to electronicconnector reader 615. The reader may include an RFID reader circuit thatgenerates the excitation signal to activate the particular tag andelectrical switches which select the particular combination ofelectrode(s) nearest the particular connector 26.

In a further example, patchcords incorporating conductive elements maybe connected between the switch 100 input/output ports and transmissionequipment such as line cards, optical amplifiers, routers anddemultiplexers. The conductive elements of these patchcords are incommunication with the tag reader circuit 615 and switch controller 70.By attaching RFID tags on this transmission equipment, in a physicallocation adjacent to or on the connector receptacles on the transmissionequipment, these tags can be read remotely by tag reader circuit 615through the conductive elements of the patchcords. These patchcordsserve to extend the traceability of connections from the switch 100 outto the equipment attached thereto. The switch controller 70, interfacedto the Operations Support Systems (OSS), enables an inventory ofphysical fiber optic connections to be ascertained and updated asneeded.

Example: Power Monitoring

In addition, the optical power transmitted through any particularoptical fiber may be monitored by use of a shared, non-invasive opticalpower monitor head integrated within the end of the gripper 50, forexample (FIG. 19). When the optical power monitor head guides the fiber20 into a shaped-channel containing deflection element 134 to produce amicro-bend 133, a small amount of light is coupled out of fiber 20 ontothe photodiode element 135. The clamping element 134 may include narrowslots that enable the spring element 23 to preferentially pass andseparate from fiber element 20. The micro-bend 133 is produced inoptical fiber 20 alone and thereby the spring element 23 does notinterfere in the detection of out-coupled light. For the particularfiber, coating and jacket type used in the flexible circuitconstruction, the optical signal within the fiber can be inferred fromthe power level of the out-coupled light and thereby calibrated.Cross-connect switches with substantial numbers of ports (>100's)benefit from the ability to share a single detector 135 across an entirearray of ports.

Typically, optical power is measured at either the proximal end of fibernear the input terminal array 170 as in the above example, oralternately at the distal end of the fiber 81 exiting flexible circuitstack 40. At this location, fibers 20 are separated from spring elements23 and are preferentially oriented along a substantially linear array tofacilitate independent physical probing of any fiber 20.

In an alternate embodiment, tap-integrated photodetectors, such as thosecommercially supplied by Santec, JDS Uniphase, etc., can be attached,fusion spliced or connected to one or more fibers 81 within the opticalswitch to monitor optical power passing through the fiber and incommunication with controller 70 to report back optical power readingsthrough the user interface. These tap-integrated photodetectors monitora small amount of power while the majority of light passes through,having a typical insertion loss of 0.5 dB. Single fiber photodetectorscan be provided individually, or arrays of photodetectors can beprovided in a single package.

The optical power readings are typically reported back through a SimpleNetwork Management Protocol (SNMP) software agent to the network'sOperational Support Systems (OSS). The OSS is a software system whichmonitors, manages and controls the large number of network elementscomprising the communications and/or computing network.

Example: Interposed Array of Docking Ports

In a further example of the cross-connect system, a single three-axisactuator with statically positioned input terminals may also be used toreconfigure any flexible circuit in a no-blocking fashion byincorporation of an array of connector holders interposed between inputarray of connector receptacles which serve as temporary docking ports.Such docking ports may be substantially similar to a half-section of atransversely divided union adapter. This approach offers the potentialto eliminate the need for lateral displacement of the connector rows atthe input array 170.

In this particular example, the docking ports are disposed in a regular,spaced-apart pattern intermediate and between columns and rows of theinput terminal array. Moreover, in this example, contrasting withprevious examples, the positions of input terminals are fixed, i.e.,they do not require shuffling on a row-by-row basis as in previousembodiments. To move the connector across the column, the gripper mustplace the connector into a temporary holding or docking port, whichfrees the gripper to exit the column and enter/descend into an adjacentcolumn, where it disengages the connector from the docking port andcontinues on with the next incremental translation step. The dockingports on either side of the connector column allow the gripper to shiftthe connector to the midpoint with next column, the extract the gripperfrom this column and insert it back into this next column where it canreengage connector and continue to the next move.

Example: Multiple Linear Actuation Columns

In an alternate example, one dedicated actuator per connector column isutilized. FIG. 20 schematically illustrates a side view of the approach,comprised of actuators interposed between all or a subset of the inputterminal connector columns. Actuators 525 utilize, for example,motorized lead screws or ball screws 531 which raise or lower rotatableplatforms 527. Motors 534 attached to outer sleeve of actuator andsubstantially surrounding ball screw 531 produce rotation of platforms527. Actuators may remain within columnar interstitial spaces, or theymay ascend vertically to exit the switch active volume.

Reconfiguration of fiber optic connectors 26 is achieved by multiplelinear/rotary actuators with independent grippers. In this example, afiber optic connector 26 and floating carrier 528 are shuffled betweenparallel and synchronized linear/rotary actuators 525-1, 525-2, 525-3.The carrier 528 is held in alternation by grippers 525-1, 525-2, 525-3.

A related actuation implementation is illustrated in FIG. 21. The staticoptical output ports 180 occupy an upper section of the switch 100volume and the reconfigurable input terminals 170 occupy a lower sectionof the switch volume. One or more grippers retained at the ends oftranslatable linear actuators descend and maneuver between columns ofconnectors in a sequence of steps to engage a particular fiber connectorreceptacle, remove it from a connector receptacle and move the fiberconnector across the input array of fiber ports without interfering thesubstantial numbers of surrounding circuits. Vertical movement throughthe array is achieved by raising or lowering the particular gripperholding the connector. Vertical motion occurs within the space betweencolumns of connectors parallel to the one dimensional switch backbone.Therefore, vertical motion up or down multiple rows may be achieved in acontinuous fashion.

In a particular embodiment, a pair of independently movable grippers653, 654 extend into the interconnect volume, pass down through theclear access regions between columns of receptacles 30 populated withconnectors 26, and latch onto a floating connector carrier 651 thattransports a connector 26 from one port to another. The linear actuators655 and 656 raise and lower grippers 653 and 654. Motors 671 and 672provide rotation of the linear actuators 655 and 656 by +/−90 degrees,thereby orienting elongated grippers so that they may pass betweencolumns without interfering with adjacent flexible fiber optic circuits21 attached thereto. Grippers 653 and 654 rotate back 90 degrees oncethey reach the desired level and re-attach to carriage 651. Theactuators 656 and 655, in their fully extended positions, extend intothe free space behind upper set of switch ports 30′. The fibers 20emanating from these ports are routed around the actuators and interfacethe fibers within multilayer circuit stack 40.

In a further example, the speed of the optical switch is increased byincorporating fast 1×2 optical switches before one or more of the inputterminals and after one or more of the output ports. These opticalswitches may fiber-coupled and based on a magnetooptic, thermooptic orelectrooptic response, for example, with switching speeds ranging from50 ms to <1 ns. Switching between two cross connect configurations canbe achieved without interruption of optical signals by synchronizedbypass switching of a pair of 1×2 optical switches to switch between twocross-connect circuits.

Generalized Cross-Connect Systems

The optical cross-connect switch apparatus and systems described hereinare based on unique geometric arrangements of physical interconnectionsand reconfiguration algorithms to transform these physicalinterconnections in a non-blocking and ordered manner. The followingsections disclose the fundamental mathematical aspects and topology ofthis interconnect system.

In this invention, the fiber strand interconnection volume lies betweentwo planes spaced apart by a distance L. The first plane coincides withan input terminal array and the second plane coincides with anintermediate array. Only the connections made to input terminal arrayare reconfigurable. Three classes of all-fiber interconnect geometriesare of particular interest: those interlinking (1) a two-dimensionalarray of input terminals and two-dimensional array of intermediateports, (2) a two-dimensional array of input terminals andone-dimensional array of intermediate ports, and (3) a one-dimensionalarray of input terminals and one-dimensional array of intermediateports. The input terminals generally include reconfigurable connectorswhich mate with connector receptacles and the intermediate ports consistof an array of fiber guides at switch backbone 41 through which thefiber lines pass under tension to the modular tensioning and slackelements 40.

The group of fiber interconnections are described in terms of a BraidGroup, with an associated algebra well suited to represent the variousgeometrical relationships between interconnect strands making-up abraid. Each fiber line or circuit bridging the input and intermediateplanes is mathematically equivalent to a strand joining two points. Thecross-connect switch volume is comprised of large numbers of strandswhose geometric relationships are dynamic. Techniques to avoid knottingof these strands is based on their crossing characteristics in relationto other strands. One would like to develop an interconnection topologyand reconfiguration algorithm to take one end of a particular strand atthe input plane and maneuver its endpoint such that the strand passesthrough the interconnect volume without entangling other strands.

The set of N switch interconnections characterizing a particular switchstate is represented by an N-stranded braid. The braid generator t_(i)is defined over the braid group and represents the physical crossing ofa strand at positon i over a strand at position i+1 (FIG. 22A). Forexample, a braid group of n strands 21″″ may be denoted by B_(x)=(t₁, .. . , t_(n)). A particular braid element of this group is described by aproduct of t_(i)'s, where the terms in the product are ordered fromright to left to correspond to crossings arranged from right to leftalong each strand 21″″. The subscript i refers not to a physical strandbut to position within the braid.

Based on the properties of braid groups, two crossings commute only ifthey do not operate on the same strand. That is, t_(i)t_(j)=t_(j)t_(i)if |i−j−>1. Therefore, the usual notion of commutativity undermultiplication does not apply to the braid generator. A knot occurs whenone strand fully wraps around another and is represented by a generatort_(i) ² (FIG. 22B). One strand simply passing over another (representedby t_(i)) does not represent a knot, because strands can be thought ofas lying in different layers, one layer on top of another. In general, astrand including the generator t_(i) ^(x), where x>1, would exhibit aknot.

It is a requirement of all-fiber cross-connect systems thatinterconnections remain knot-free. Such interconnections correspond tobraids comprised of strands with |x|<=1 and are conventionally calledpositive (x>0) or negative (x<0) non-repeating braids (positive if thebraid only has positive crossings, that is, the front strands have apositive slope). To prevent physical entanglement within the switchinterconnect volume, it is necessary that each strand be described bygenerators t_(i) ^(x) with |x|<=1. An example of a negative,non-repeating braid is given by (t₁ ⁻¹t₂ ⁻¹k t₁₆ ⁻¹)(t₁ ⁻¹t₂ ⁻¹k t₁₅⁻¹)k (t₁ ⁻¹t₂ ⁻¹)t₁ ⁻¹ and illustrated in FIG. 23. While this braidincludes the product of a number of generators t_(i) ⁻¹ on the samestrand position i, it does not include t_(i) ^(x) with |x|>1 because ofnon-commutativity. Therefore, each strand 21″″ can be thought of asresiding in its own layer, which can be individually peeled away fromother layers.

Geometry 1: 2-D Array to 2-D Array

In a first cross-connect switch geometry, physical fiberinterconnections 21″″ join the terminals of a two-dimensional inputarray 170 and a two-dimensional intermediate array 181. Assume there area columns by b rows at both the input array and the intermediate array.In general, the number of rows and columns can be dissimilar; in fact,it may be advantageous for some applications that the input array tohave a larger number of terminals than the intermediate array has ports.There may be additional docking ports at the input array, for example.Moreover, consider the case in which all circuits have the same fixedlength l, which is greater than the spacing L between the two arrays.

A fiber optic connection at the front input terminal array isreconfigured by physically translating its proximal endpoint within theinterstitial regions 108′ between the arrayed interconnections of theinput terminals. This endpoint should remain close to the plane of theinput array because interstitial gaps between interconnects exist hereand they allow physical access for a pick-and-place actuator, forexample, to extend and reconfigure endpoints. On the other hand, theinterconnects' distal endpoints attach to the intermediate array andtheir configurations remain fixed. There is generally not anunobstructed path for an actuator to move from the input array to theintermediate array through the intervening interconnect volume, so allreconfiguration is performed in proximity to the input array.

Fiber interconnects represented by an N-stranded braid can realize aninfinite number of configurations. If the interconnect paths 21″″ arespatially indeterminate, as would be the case when the length of thestrand is greater than the straight-line path, the knotting of strandsis possible (FIG. 24). This particular illustration corresponds to a16×16 cross-connect. Excess interconnect lengths within the volumeresult in indeterminate crossing points, potential knotting andexcessively sharp bending of interconnects.

Least-path, variable length interconnects must be maintained to preventknotting. To manage these excess fiber lengths, the tensioning andstorage volume 138 with flexible circuit modules 40 is provided, locatedopposite the intermediate plane and adjacent to the strand volume 108(FIG. 25). Each interconnect state is then comprised of onlystraight-line strands 21″″ joining the input 170 and intermediate 181arrays, as shown in FIGS. 26A and 26B. We assume the fiberinterconnections have infinitesimal thicknesses so that deviations fromlinear paths at potential crossing points have a negligible effect onthe interconnection trajectory. Mathematically, this set ofinterconnections belongs to the group of positive (or negative)non-repeating braids. The sign of the braids is dictated by an initialordering convention, which must be maintained during all subsequentreconfigurations. For positive braids, the strand i passes over thestrand i+1 when viewed from the side, as in FIG. 22A.

Assuming each interconnect follows a straight-line path, there is adeterministic algorithm to move the endpoint of one strand through theinterconnect volume to a new state, such that the strand and all otherstrace straight-line paths in the final state. An example reconfigurationfrom an initial port A to a final port B, following a path shown as adotted line in the vicinity of the input array, is illustrated in FIG.27. To simplify this analysis, only one intervening strand is shown.

To ensure that the strand 21-1″″ corresponding to the vector {tilde over(R)}₁ still follows a straight-line path after translating todestination port B, its moveable end must pass above or belowintervening interconnections in a calculated fashion through the sharedvolume. The moves are based on computations taking account of thelocations of all other strands. The endpoints of an intervening strand21-2″″ joining the point (x₂, y₂, 0) within the input plane and thepoint (x′₂, y′₂, L) of the intermediate plane define a vector {tildeover (R)}₂, the equations of which, parameterized here in s, are givenby:

{tilde over (R)}=

X₂, Y₂, Z₂

  (1)

X ₂ =x ₂ +s(x ₂ −x′ ₂),   (2)

Y ₂ =y ₂ +s(y ₂ −y′ ₂),   (3)

Z ₂=−sL   (4)

Similarly, the endpoints (x₁, y₁, 0) and (x′₁, y′₁, L) define a vector{tilde over (R)}₁ corresponding to strand 1:

{tilde over (R)}₁=

X₁, Y₁, Z₁

  (5)

X ₁ =x ₁ +s(x ₁ −x′ ₁),   (6)

Y ₁ =y ₁ +s(y ₁ −y′ ₁),   (7)

Z ₁ =−sL   (8)

Strand 1 must follow a path through the volume such that its final stateis a straight-line, disentangled from other strands. This path isdetermined by solving for (Y_(1,o), Y_(2,o)), which are the relativeelevations of strands 1 and 2 respectively, when strand 1 is at itsdestination terminal and when the vertical (y) projection of strands 1and 2 cross, so that X₁=X₂ and Z₁=Z₂. When the X-positions are equal,the parameter s_(o) is given by:

$\begin{matrix}{{s_{o} = \frac{\left( {x_{1} - x_{2}} \right)}{\left( {x_{2} - x_{1} - x_{2}^{\prime} + x_{1}^{\prime}} \right)}},} & (9)\end{matrix}$

so that the elevations of each strand at this location are given by:

y _(1,o) =y ₁ +s _(o)(y ₁ −y′ ₁),   (10)

y _(2,o) =y ₂ +s ₀(y ₂ −y′ ₂).   (11)

The requirement to reconfigure strands while preventing entanglement isthen dictated by the following conditional relations: ify_(1,o)≧y_(2,o), strand 1 passes above strand 2, and if y_(1,o)<y_(2,o),strand 1 passes below strand 2. This ensures that after reconfigurationand for strands of infinitesimal thickness, strand 1 follows astraight-line path unencumbered by strand 2. By induction, applying thiscondition to all other intervening strands would ensure that strand 1follows a straight-line path throughout the entire interconnect volume,for any number of intervening strands.

FIG. 28 illustrates a further example of circuit reconfiguration for tworather than one intervening strand. In this situation, the input end ofstrand 1 must move above strand 2 to satisfy the above condition andfollow a straight-line to the destination terminal. While this algorithmensures that the final state is a straight-line, it does not guaranteethat the strand follows a straight-line in those intermediate statespassed through during reconfiguration. The locations of otherintervening strands may place conflicting requirements on suchreconfiguration. Physical interference with intermediate strands such as3 can occur during the intermediate states, and as a result, thelocation of intermediate strands will be perturbed. Strand 1 21-1″″ may“kink” 221-1 due to interference with strand 3 21-3″″ while passing overstrand 2 21-2″″. For substantial numbers of strands, the number anddegree of kinks may be significant. The amount of perturbation willdepend on the force balance between interacting strands. Therefore, theintermediate configuration of strands is not obvious and must be solvedself-consistently for each intermediate state based on the knowledge ofthe tension in all strands.

In practice, it is difficult to precisely control the tension for largenumbers of interconnections. Tensioning is produced, for example, byspring-loaded take-up spools that retain excess interconnect lengths andkeep the strands taut through the intermediate ports. Each strand mayexperience different tension depending on its extended length and thedegree of wear and friction. Considering these practical concerns, it isnot possible to prove unequivocally that tangling or excessive bendingof the strands will not occur during repeated reconfiguration.

For straight-line interconnections, the length l of strands connectingports ranges between bounds according to: L²≦I²≦(adx)²+(bdy)²+L². Thenon-straight-line paths during intermediate reconfiguration states mayrequire a non-negligible additional length during reconfiguration. Thesystem of 2-D to 1-D arrays of interconnects described next overcomesthese various limitations.

Geometry 2: 2-D Array to 1-D Array

The geometric “order” of strands within the interconnect volume isincreased by interconnecting the 2-D input array of terminals 170 to a1-D intermediate array of ports at backbone 41. By “order” we refer tothe partitioning of the switch volume into smaller columnar regions thatare physically independent of one another. Arbitrary interconnectionsare reconfigured by crossing through each independent, orthogonal zonein a sequential fashion. For this geometry, straight-lineinterconnections are maintained even during reconfiguration. The inputarray consists of a columns by b rows and the intermediate arrayconsists of n=a·b rows.

For example, the interconnect strands between a 4 x 4 terminal inputarray 170 and a 16×1 port intermediate array 41 is shown in FIGS. 29Aand 29B. The strands 21″″ follow straight-lines between the inputterminals and intermediate ports. The mapping of the 2-D intermediatearray in the earlier example to a 1-D array performs the mathematicalequivalent of “combing” the interconnection braid. The interconnectiongeometry reduces to a deterministic arrangement that eliminates thepotential for circuit interference by subdividing the braid intoseparate, independent subbraids or zones 101-1, 101-2, 101-3, 101-4originating from each column of input terminals. That is, B_(n)=(t₁,Kt_(n)) reduces to the subbraid group B_(a)=(t₁,K t_(a)), where a is thenumber of rows. The interconnections are inserted and maintained in theproper order such that each subbraid is non-repeating—any two of itsstrands cross at most one. The strands 21″″ of the non-repeating braidare overlaid back to front without intertwining and effectively liewithin separate layers, thus eliminating the tendency to tangle.

This cross-connect geometry has several unique advantages. Strands donot span more than one zone for any particular configuration or at anytime during the reconfiguration. This eliminates the indeterminismafflicting the 2-D to 2-D interconnections. The algorithms to re-arrangeany interconnect in a non-blocking fashion require knowledge of eachinterconnect's intermediate array row m and the sign of the braid. Tomove a strand n within column i to a column j, the subset of strands incolumn i lying between strand n and strand j must be identified, afterwhich the proximal endpoint of this strand traces out a continuous pathpassing below the subset of strands with m>n and above the subset ofstrands with m<n.

A fiber optic cross-connect system including of a four-by-four terminalinput array 170 that separates into zones 101-1, 101-2, 101-3 and 101-4is shown schematically in the perspective view FIG. 29A and top viewFIG. 29B. The two-dimensional array of self-tensioning circuits 21mapped into a one-dimensional array or backbone 41 with substantiallystraight-line paths there between partitions the switch interconnectvolume 108 into multiple independent, non-interfering zones 101. Thefiber circuits 21 lie at the nominal centers of such zones. Thisimposition of topological order on the three-dimensional arrangement ofarbitrary circuit connections results in the separation and retention ofoptical circuits 21 within substantially spaced-apart regions. Theresulting geometrical placement of each circuit 21 enables any number ofarbitrary terminal reconfigurations to remain non-blocking andinterference-free for reconfiguration governed by a series of rules andactions, dependent in part on the knowledge of how the multiplicity offiber circuits 21, labeled 1 . . . 16 at backbone 41, map to the rowsand columns of input array 170.

The rules governing non-blocking circuit re-arrangement are as follows:

-   -   I. Fiber circuits 21 must follow substantially straight-line        paths between the two-dimensional input terminal array 170 and        the one-dimensional port backbone 41.    -   II. Fiber circuits 21 must span only one zone 101 for any        particular configuration.    -   III. Each fiber circuit must be associated with unique “address”        relating to its elevation at the fiber backbone 41.    -   IV. A fiber circuit must be inserted or removed from a column        only in an ordered fashion based on each circuit's “address”        within fiber backbone. Circuits within a particular zone may be        thought of as occupying separate “layers” within the zone along        vertical planes joining the input column and the backplane.        These layers are ordered sequentially based on the “address” of        the fiber circuit within, in either a positive or negative        ordering.

The actions required to re-arrange any circuit in a non-blocking fashionare as follows:

-   -   Movement of a particular fiber circuit 21 across a column        requires knowledge of each fiber circuit's “address” m and        “order”. To move a circuit n within column i to a column j,        first identify which subset of circuits in column i lie between        circuit n and column j, then move below the subset of fiber        circuits with m>n and above the subset of fiber circuits with        m<n on a column by column basis.

Reconfiguration of circuits laid out according to the geometry disclosedherein and following the rules outlined above can be achieved in anon-blocking and non-interfering fashion. Reconfiguration only requiresknowledge of the particular state of switch at the time ofreconfiguration and is independent of prior switch history. Thisrule-based algorithm remains valid for any number of switchreconfigurations.

For illustration by way of a simplified example, the reconfiguration ofa circuit which must pass from zone i−1 to zone i+1 by traversing anintermediate zone i (101-i) in a manner which avoids entanglement ofcircuits 21 is shown in FIG. 30A. In the initial configuration, thecircuit 21′ undergoing reconfiguration is initially attached to terminalA within zone i−1, and is to be moved to terminal B within zone i+1 ofinput array 170 in a non-blocking fashion. If the circuit 21′ isreconfigured by moving it from terminal A to terminal B along astraight-line path lying substantially in a plane parallel to 170, asshown in FIG. 30B, the circuit 21′ becomes physically entangled with thecircuits of zone i. This entanglement will prevent subsequentreconfiguration through the knotted region. The proper path of circuit21′ to prevent physical entanglement is illustrated in FIG. 31A, whereinthe circuit 21′ passes below those circuits 21 originating from a higherlevel at the switch backbone 41 and above those circuits originatingfrom a lower level at the switch backbone.

In the particular example illustrated in FIG. 31A, a strand passes fromcolumn i−1 to column i+1 by traversing an intermediate column i in amanner that avoids entanglement. If the strand were reconfigured bymoving the end of strand i from a terminal A to a terminal B along adirect straight-line path in the plane parallel to input array, thestrand 21-j″″ would likely become physically entangled with otherstrands of zone i. Entanglement prevents subsequent reconfigurationthrough the knotted region. A proper path 111 of the strand endpoint isrepresented by the dotted line in FIG. 31A, wherein the strand passesbelow those strands originating from a higher level at the switchbackbone and above those strands originating from a lower level at theswitch backbone.

Since the strands within any column have a non-repeating braidstructure, each strand 21″″ occupies its own layer 175 that can beindividually peeled back from the others. FIGS. 31B and 31C illustrateend-on views of strands within the zone i. In this representation, thecircuit j passes between these separate layers corresponding to strands8 and 10. Such a path 111 does not cross nor entangle adjacent strands.

Placement of circuits within each column requires adherence to orderingconventions in accordance with Rule IV above. FIGS. 31B and 31Cillustrate two alternative implementations of the ordering rule,corresponding to positive and negative braids, respectively. Thisfigures are not-to-scale and represent an exploded view down the z axisof a particular zone 101-i in FIG. 31A to reveal the ordering ofcircuits 21 therein. A positive braid (FIG. 31B) or ordering rulerequires that fiber circuits 21 be ordered from left to right withineach zone 101 with increasing addresses (or elevations) at the onedimensional backbone. A negative braid (FIG. 31C) or ordering rulerequires that fiber circuits 21 be ordered from left to right withineach zone 101 with decreasing addresses (or elevations) at the onedimensional backbone 41. The trajectories to reconfigure circuits forthese two different order conventions are different.

FIG. 34A illustrates the terminal-map 110 and reconfiguration trajectoryto move a circuit from a terminal A to a terminal B within the array ofinput terminals 170 in which the interconnections are ordered accordingto a positive braids. This terminal map 110 corresponds to a 10 columnby 14-row array of terminals, wherein the numbers associated with eachterminal correspond to the address of the particular circuit 21 attachedthereto. Each fiber circuit 21 within the column originates from adifferent level of backbone 41 and is associated with an address used todetermine the proper non-blocking trajectory for the circuit. In thisparticular example, each terminal has been randomly assigned a circuit.A first fiber circuit at terminal A (col,row)=(1,6) is to be switched toport B (10,4). A second circuit presently at port B is moved to adocking port (not shown) to vacate port B. As shown in FIG. 34A, to movethe first circuit from left to right across this array of ports, it mustpass through each column or zone 101-1, . . . in a sequential fashionwithout entangling any potentially crisscrossing circuits within thecolumns.

To trace out a non-interfering path through the array of fiber circuits,the particular circuit A must follow a path across the columns ofconnectors and their attached fibers, whereby fiber circuit A passesbelow those optical circuit elements which originate from higher levelsat the backbone and pass above those elements which originate from lowerlevels. The path represented by FIG. 34B represents the relative motionsof the various circuits. The actual trajectory is dependent on theparticular actuation approach. In the particular embodiment of theinvention utilizing shuffling connector rows 46, the path shown in FIG.34B is actually comprised of both gripper 50 motion and independentsliding of each connector row 46 along the row axis 58. The gripper 50actually translates up and down columns in a straight-line path, withthe rows 46 shifting transversely to ensure that the particular fibercircuit 21 moves to the left or right of each other circuit within thecolumn. In this example, the circuit moves according to a sequence ofsteps comprised of alternately descending into and ascending out ofzones. The circuit must fully clear the first zone 101-1 before enteringinto a second zone 101-2. In the sense of FIG. 34B, it should beappreciated that there is equivalence between moving above or below acircuit and moving to the left or right of the same circuit,respectively.

The movable endpoint of circuit 21′ is constrained to lie within aregion substantially parallel to and in the vicinity of the plane ofinput terminal array 170. Within this region there exist open columnarvolumes within which an actuator and gripper can extend withoutinterfering with surrounding fiber circuits.

Alternately, FIG. 34B illustrates the reconfiguration trajectory for thesame terminal map as FIG. 34A, in which the interconnections are filledand ordered as negative braids instead.

Moreover, in accordance with Rule II above, the boundaries of flexiblefiber circuits 21 within each column or zone 101 must remain within theboundaries of that zone. To illustrate this point, a side view of theparticular zone 101-1 is shown in FIG. 32A. Those flexible circuitsattached to a particular column of connector input terminals shouldoccupy their particular wedge-shaped slice, regardless of their physicallocation at the backbone 41. The width of the slice should be adequateto enable all circuits to substantially remain within its wedge-shapedboundary for all potential flexible circuit configurations and isrelated to the column-to-column spacing.

In practice, the greatest tendency for a fiber circuit 21 to extend intoneighboring zone 101-2 is the configuration for which all circuits 21within a zone 101-1 cross at the same point 105. The location of point105 is midway between input array 170 and backbone 41. The width of thezone 101-1 at this location is equal to half the column-to-columnspacing of input terminal array 170. The greatest density of fibercircuits within each wedge occurs for the particular configurationwherein the circuits from the linear backbone are mapped to verticallyinverted positions as illustrated in FIG. 32B. In this case, thecrossing point of all fiber circuits is concentrated at a singlecentrally located region 105 within the switch volume. The area of asubstantially square bundle comprised of all flexible fiber opticcircuits 21 crossing at this central location should fit within thevolume defined by the boundaries of this wedge-shaped zone 101-1.

The density of circuits within region 105 can be reduced bydiffusing-out the crossing points over a larger volume 105 that stillremains within the substantially wedge-shaped boundaries of theparticular zone. This is achieved, for example, by horizontallystaggering the fiber guides or ports 45 at the switch backbone 41 whileretaining the one-to-one mapping of each circuit 21 to its elevation atthe backbone. Alternatively, the direction of the major axis of theswitch backbone 41 can be made non-parallel to the axis of the inputcolumns 101 to distribute crossing points over an expanded region of thezone. Alternately, the horizontal and/or vertical spacings of the inputconnector array 170 can be made irregular to add spatial disordersufficient to expand region 105.

In a particular example, the horizontal spacing between adjacent columnsof input connector terminals is 25 mm, each column is comprised of 100rows or terminals, and the outer diameter of each flexible fiber opticcircuit is 1 mm. Therefore, the cross sectional area of hexagonallyclose packed fiber optic circuits passing through the crossing point isless than or equal to 85 mm². For a substantially square cross-section,the dimensions of such a fiber bundle is about 9×9 mm. For awedge-shaped zone, the width at its center is about 12.5 mm. Since thewidth of the fiber bundle (˜9 mm) is less than the width of theparticular zone (˜12.5 mm), the density is below this maximum, asdesired to prevent physical interference or blocking. In practice, thedensity of circuits would be lower since the crossing points aregenerally dispersed or uniformly distributed across the wedge-shapedregion for random interconnections between ports.

Similarly, FIGS. 32A and 32B illustrate an additional subbraid typegermane to the analysis of entanglement. The upper diagram illustratesthe identity brade E. Inversion of the y axis of the 1-D intermediatearray generates the twisted braid shown in the lower diagram.Physically, this braid represents a cross-connect zone or column withhighly mixed interconnects. The braid is nevertheless equivalent to thenon-repeating braid represented in FIG. 22, where the crossing pointshave been translated along the strands to reveal the characteristiclayering of non-repeating (non-tangled) braids.

Until now, we have assumed that each strand has an infinitesimalthickness, or each layer is infinitesimally thin. However, the physicalthickness is relevant to determine the ultimate density limit fordisentangled interconnects and the maximum number of cross-connect portsachievable within a given volume. The braid of FIG. 32B is useful tothis end because it produces the highest strand density within alocalized volume 105 about the crossover point. The physical thicknessof the crossover point depends on the physical diameter of the strandsand can be stretched as wide as b·d_(o), where d_(o) is the diameter ofa strand and b is the number of rows of the input array (FIG. 33A).However, since each strand is under tension, the strands willreconfigure back into a bundle to achieve a least-path configuration asshown in FIG. 33B. The outer-most strands collapse onto the central axisto reduce their length. Assuming the strands form a loosely packed bunchwith a circular perimeter, the diameter of the crossover is equal to

$D = {2d_{o}{\sqrt{\frac{b}{\pi}}.}}$

If all b interconnect subbraids are similarly ordered, the crossoverpoints within each zone will be in alignment along a common lineparallel to x. Therefore, the spacing between each subbraid at this linemust be greater than or equal to D to prevent interference betweensubbraids. The number of strands is given by:

$b = {{\pi \left( \frac{D}{2d_{o}} \right)}^{2}.}$

For typical values (D=12.5 mm, d_(o)=0.6 mm), there may be up to b=340strands per braid. Patch-panels typically have 12 to 18 columns ofconnectors per rack, so the cross-connect has the potential to scale upto about 6120×6120 connections based on this geometry.

The maximum time to reconfigure a port for this 2-D to 1-D array ofinterconnections is proportional to the length of the reconfigurationtrajectory ˜b·a=N. The numbers associated with the 2-D array of inputterminals in the top figure correspond to the vertical addresses of eachstrand at the 1-D intermediate plane. The maximum reconfiguration timecorresponds to the case in which a strand endpoint must travel up anddown each column of the array. The reconfiguration algorithm computes aminimum length reconfiguration path, skipping those columns or strandsthat do not require unweaving, such as column 4 and much of column 5.

The volume of this switch system scales gracefully as N and the widthand height of the input array are a·dx and b·dy, respectively. Thevertical spacing of the N interconnects at the back plane is small sinceconnectors are not required at this location. As a result, the verticalsize of this switch implementation is limited by the size and spacing ofthe input array and is equivalent to manual patch-panels.

In this example, the interconnects maintain straight-line paths at alltimes and their length l is bounded by:

$L^{2} \leq I^{2} \leq {\left( {\frac{a}{2}{dx}} \right)^{2} + \left( {b\; {dy}} \right)^{2} + {L^{2}.}}$

This geometry minimizes the amount of fiber that must be retained on thetensioning take-up spools in comparison to Example 1. The interconnectstructure that arises for this switch geometry also provides modularity,so that interconnections can be added and/or replaced. The system uses aseries of stacked modules (corresponding to a block of interconnects)that can be added incrementally. The interconnect strands correspondingto a block of rows at the intermediate port array can be removed, evenfrom the middle of the stack, without disrupting other interconnections.The resulting gap left after removing the block is collapsed verticallyand a replacement block of interconnects can be re-inserted at the topof the stack.

Geometry 3: 1-D Array to 1-D Array

In an alternate all-fiber switch arrangement, the all-fibercross-connect is structured such that interconnect strands bridge aone-dimensional array with N rows at the input plane 170 and aone-dimensional array 41 with N columns at the intermediate plane. Thisconfiguration retains the desirable non-tangled characteristics of theprevious example, with each interconnect following a deterministic,straight-line path during and after reconfiguration. The one-dimensionalarrays are oriented perpendicular 41 (FIG. 35A) or parallel 41′ (FIG.35B) to one another.

The reconfiguration algorithm for this geometry is similar to that ofthe previous example. For the arrangement in FIG. 35A, interconnects arereconfigured in accordance with their elevations at the intermediatearray, passing above those interconnects originating from a lower leveland below those interconnects originating from a higher level. Anexample reconfiguration is illustrated in FIG. 36, where the dotted lineindicates the path 111 followed by the endpoint of the strand 21″″.

Similarly, the two 1-D arrays can be oriented parallel to one another,with the strands ordered according to their locations at theintermediate 1-D array. The interconnects will have a tendency to form athick bundle at the center of the interconnection region, similar tothat illustrated in FIG. 33. The presence of a single, dense crossover105 bundle requires minimization of surface friction between strands.This is a disadvantage compared to the 2-D to 1-D array example, forwhich the crossovers were less densely distributed.

The time to reconfigure a port is also proportional to N, the totalnumber of ports. Ports can be added incrementally by concatenatinginterconnects and ports to the ends of the array. The minimum spacingfor each reconfigurable port in the input array is typically 5 mm toallow adequate space for a fiber optic connector body. Therefore, withinthe footprint of manual patch-panels, this approach is practicallylimited to less than 500 ports.

In conclusion, the reconfigurable, all-fiber system of interconnectiondisclosed herein exhibit ideal optical characteristics and can berealized in various geometries. The optimal geometry to prevententanglement utilizes a 2-D input terminal array and a 1-D intermediateport array. Various algorithms have been developed to reconfigure suchinterconnections in a completely arbitrary fashion and without limits.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bounds of the appendedclaims.

1: A fiber optic patch panel system for the ordered changeablearrangement of a fiber optic interconnection braid, comprised of: amultiplicity of subbraids, each subbraid including a multiplicity offiber optic interconnection strands; a two-dimensional array of fiberoptic union adaptors aligned in spaced apart rows and columns within acommon plane and providing changeable, low loss interconnection of thestrands within the subbraids between the front-side cables and back-sidecables connected thereto; each row of adaptors being physically detachedfrom the other rows and free to linearly translate within its row from anominal central column position by less than a column width in eitherdirection, with strands connected to the adapters; the system includingindependent linear actuators each coupled to a different row ofadaptors, and wherein the system further includes a processorcontrolling the adaptors and selectively operating the rows of adaptorsin relation to existing strands between front-side cables and back-sidecables to facilitate the reconfiguration of non-entangling strandcombinations. 2: A fiber optic patch panel in accordance with claim 1,further including a robotic connector gripper responsive to processorcommands for moving any individual strand in a direction substantiallyparallel to, but offset from, the columns of adaptors, and theprogrammed translation under processor control of each linear actuatorfor reconfiguration of the individual strand is accomplished inprogrammed relation to the columnar motion of the robotic gripper. 3: Afiber optic patch panel system in accordance with claim 1, in which anumber of strands, in the range of 10 to 48, connect to each row ofadaptors, and wherein the translation of an adaptor in either directionfrom the nominal central position in either direction is by half acolumn width. 4: A system as set forth in claim 2 above, wherein thenumber of strands total 48 to 2048 and each strand follows asubstantially straight line path between front-side cables and back-sidecables coupled thereto. 5: A system as set forth in claim 4, wherein thelength of each straight line path is 2 meters or less. 6: A system asset forth in claim 2, wherein the individual strand is moved by therobotic gripper such that the individual strand is not physicallyimpeded by other strands. 7: An optical fiber patch panel managementapparatus providing orderly and deterministic fiber strand routingwithin a limited volume, comprised of an arrayed multiplicity of opticalfiber strands each in a substantially straight-line configuration,spanning an interconnect volume from an adjacent planar input side to astorage volume side, said storage volume side containing a multiplicityof fiber strand tensioning and storage elements spaced apart in threedimensions, the optical fiber strands being continuous in lengththerebetween, and the management apparatus comprising: a multiplicity ofinput terminals arrayed in two dimensions along the planar input side ofthe interconnect volume for receiving and coupling to the proximal endsof the optical fiber strands; an array of circumferential through portsalong the plane separating the interconnect volume and the storagevolumes, the through ports including low friction surfaces guidingoptical fiber strands; and a multiplicity of arrayed fiber strandtensioning and storage elements in the storage volume side configured tovary fiber strand lengths sufficiently to maintain the fiber strands ina substantially straight-line configuration within the interconnectvolume. 8: An arrayed collection of optical fiber strands in accordancewith claim 7 wherein the optical fibers are small diameter plasticcoated single mode or multimode fibers with outer diameters of less than1 mm. 9: An arrayed collection of optical fiber strands in accordancewith claim 7 wherein the array of through ports is substantiallyone-dimensional. 10: An arrayed collection of optical fibers inaccordance with claim 9 wherein the number of input terminals is greaterthan or equal to the number of substantially straight-line opticalfibers. 11: An arrayed multiplicity of optical fibers in accordance withclaim 9 wherein the substantially straight-line configuration of eachoptical fiber may comprise arced segments of limited length with greaterthan a minimum bend-radius at the terminal array and throughput portarray.